Rheological and Transport Analysis of Micronized Coal-Water Suspensions Prepared in Conventional and High-Speed Stirred Ball Mills

  • Rajendra K. Mehta
  • John A. Herbst


The purpose of this paper is to compare the rheological properties of micronized coal-water suspensions (CWS) prepared in different grinding devices. This hypothesis is based on the theory that the interaction between particulate phase and the nature of forces prevailing in the mill affects the particle size distribution and shape of particles. The grinding devices used were conventional tumbling ball mill and high speed stirred ball mill having pin and disc option. Flow properties of the suspensions were found to differ appreciably at desired fineness of grind (d80). This was explained on the basis of packing density and morphology of particulate phase. Typically, the high-speed stirred ball mill produced broader particle size distribution yielding distribution modulus (DM) of 0.213 as opposed to 0.384 for the conventional mill. Rheological data collected on a typical distribution constructed based on the Farris analysis revealed that suspensions were most viscous for particles ground in the pin device followed by the disc device and the conventional mill. A simple theoritical analysis has been presented to estimate the shear rate in the vicinity of the tips for the stirred ball mill under typical operating condition for this type of application. This resulted in an estimate of 680 sec−1.

Viscosity data was correlated to the shape factor of particles ground in different grinding devices. Finally, an analysis of pumping power requirement was carried out under typical fluid flow conditions utilizing rheological data which showed that suspensions ground in a stirred mill required 94.33 Hp/mile in comparison to the convention mill which required 84.13 Hp/mile.


Shear Rate High Shear Rate Rheological Data Broad Particle Size Distribution Typical Operating Condition 



Centipoise (unit of viscosity)


Volume fraction solids in slurry


Coal-water suspension


Geometric mean size of a size interval


Smallest geometric mean particle size


Largest geometric mean particle size


Pipe diameter


Distribution modulus


Maximum particle diameter


Pressure gradient along the length of pipe


80% passing size

dv/dx, γ

Shear rate


Elliptical shape factor


Cumulative weight fraction finer than size d


Friction factor


Form shape factor


Acceleration due to gravity


Newton’s constant


Coefficient of the power law model


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  1. 1.
    Rukin, E.I., Groskaya, T.P., and Delyagin, G.N., 1976, “A Study of Aqueous Suspensions of Coal in the Presence of Surface-Active Agents”, Khimiya Tverrfogo Topliva Vol. 10, No. 4, pp. 152–158.Google Scholar
  2. 2.
    Link, J.M., Laviangia, N.J., and Faddick, R.R., 1974, “The Economic Selection of a Slurry Pipeline”, Hydrotransport, Vol. 3, May.Google Scholar
  3. 3.
    O’Hara, J.B., 1976, “Coal Liquifaction”, H.C. Processing, Vol. 55, No. 11, p. 221.Google Scholar
  4. 4.
    Jinescu, V.V., 1974, “The Rheology of Suspensions”, Inter. Chem. Eng., Vol. 14, p. 397.Google Scholar
  5. 5.
    Devaney, F.D., and Shelton, S.M., 1940, “Properties of Suspension Mediums for Float and Sink Concentration”, U.S. Department of Interior, Bureau of Mines, Ri3469-R.Google Scholar
  6. 6.
    Eveson, J., 1954, “Viscosity of Suspensions”, Ind. Eng. Chem., Vol. 46, p. 1146.CrossRefGoogle Scholar
  7. 7.
    Aplan, F.F. and Spedden, H.R., 1965, “Viscosity Control in Heavy-Media Suspensions”, Proceedings VII, International Mineral Processing Congress, Vol. 1, p. 103.Google Scholar
  8. 8.
    Siddique, M., 1972, “A Kinetic Approach to Ball Mill Scale-Up for Dry and Wet Systems”, M.S. Thesis, University of Utah, Salt Lake City, Utah.Google Scholar
  9. 9.
    Mehta, R.K., 1987, “Characterization of Coal-Water Slurries Produced in a High-Speed Stirred Ball Mill”, Ph.D. Dissertation, University of Utah, Salt Lake City, Utah.Google Scholar
  10. 10.
    Stehr, N., Mehta, R.K., and Herbst, J.A., 1987, “Comparison of Energy Requirements for Conventional and Stirred Ball Milling of Coal-Water Slurries”, Coal Preparation, an International Journal, Vol. 4, pp. 209–226.CrossRefGoogle Scholar
  11. 11.
    Sommer, T.M. and Funk, J.E., 1981, “Development of a High-Solids Coal-Water Mixture for Application as a Boiler Fuel”, ASME/IEEE, Power Generation conference, St. Louis, October 4–8.Google Scholar
  12. 12.
    Mchale, E.T., Scheffee, R.S., and Rossmeissl, N.P., 1983, “Combustion of Coal-Water Slurry”, Combustion and Flame, Vol. 45, pp. 121–135.CrossRefGoogle Scholar
  13. 13.
    Funk, J.E., et al., 1981, “Preparation and Combustion of a High Solids Coal-Water Fuel CO-AL”, DOE Workshop in Coal-Water Fuel Technology, Pittsburgh.Google Scholar
  14. 14.
    Schramm, Gebhard, 1985, Introduction to Practical Viscometry Haake Viscometers, New York, p. 5.Google Scholar
  15. 15.
    Morgan, M.E., Heation, H.L., and Scheffee, R.S., 1985, “A Study of Yield Stress of CWF”, proceedings U.S. Dept. of Energy, Pittsburgh Energy Technology Center, Vllth International Symposium on Coal Slurry Fuels Preparation and Utilization, May 21–24, New Orleans, Louisiana;Google Scholar
  16. 16.
    Bird, R.B., Stewart, W.E., and Lightfoot, E.N., 1978, Transport Phenomena John Wiley & Sons, Inc., New York, p.Google Scholar
  17. 17.
    Charm, S. and McComis, W., 1965, “Determination of Yield Point for Transportation Systems”, Food Technology, Vol. 19, p. 948.Google Scholar
  18. 18.
    Henderson, C.B. and Scheffee, R.S., 1983, “The Optimum Particle-Size Distribution of Coal for Coal-Water Slurries”, Mini-Symposium, Coal Slurry Fuels, SME Annual Meeting, March, Atlanta.Google Scholar
  19. 19.
    Govier, G.W. and Aziz, K., 1972, The Flow of Complex Mixtures in Pipes, Van Nostrand-Reinhold, New York.Google Scholar
  20. 20.
    Davis, P.K., and Srivastava, P., 1982, “Rheological and Pumping Characteristics of Coal-Water Suspensions”, Journal of Pipelines, Vol. 3, pp. 97–107.Google Scholar
  21. 21.
    Wasp, E.J., Kenny, J.P., and Gandhi, R.L., 1975/77 Solid Liquid Flow Slurry Pipeline Transportatiort Series on Bulk Material Handling, Vol. 1, No. 4, Trans Tech Publications.Google Scholar

Copyright information

© Elsevier Science Publishing Co., Inc. 1990

Authors and Affiliations

  • Rajendra K. Mehta
    • 1
  • John A. Herbst
    • 2
  1. 1.Mineral Resources InstituteThe University of AlabamaTuscaloosaUSA
  2. 2.Control International Inc.University Research ParkSalt Lake CityUSA

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