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In this study,
a model for the prediction of coal particle gradation in
horizontal fluid pipeline was developed. The intent of this
study is to develop a model that can predict the coal particle
gradations in horizontal coal-liquid slurry pipelines. A
semi-empirical model originally developed by Karabelas has been
modified by applying the k-ε approach to model a dimensionless
diffusivity, originally assumed to be constant. The mechanistic
model developed shows that dimensionless diffusivity is a
function of root mean square turbulent velocity fluctuations and
many other parameters which include fluid velocity, pipe
diameter, carrier fluid and suspended particles densities,
particle size, and the efflux concentration. The modified model
was compared with four different sets of experimental data and a
CFD model, and was found to have overall good agreement. It was
employed to analyze particle gradations and the results show
that larger coal particles tend to drift to the pipe bed,
leaving the upper section of the pipes for smaller particles.
The results show that concentration profile of coal particles in
single-sized homogenous slurry is different from that of the
same particle concentration in multi-sized slurry flow for each
particle size and the same efflux concentration. The modified
model was applied to analyze the d50 concentration profile and
the result shows that d50 concentration profile represents the
actual profile accurately within low and moderate range of
particle sizes in the slurry. The mechanistic model presented in
this study will be useful for coal and other mining industries
worldwide, for accurate prediction of concentration profiles and
choice of particle sizes as well as flow velocity of slurry in
horizontal pipelines to avoid deposition and clogging of
particles along the pipeline, thereby reducing associated danger
in the pipelines. |