| Summary: | Abstract
Grinding mills are generally very inefficient, difficult to control and costly, in
terms of both power and steel consumption. Improved understanding of
temperature behaviour in milling circuits can be used in the model-based control
of milling circuits. The loss of energy to the environment from the grinding mill is
significant hence the need for adequate modeling.
The main objectives of this work are to quantify the various rates of energy loss
from the grinding mill so that a reliable model for temperature behaviour in a mill
could be developed. Firstly models of temperature behaviour in a grinding mill are
developed followed by the development of a model for the overall heat transfer
coefficient for the grinding mill as a function of the load volume, mill speed and
the design of the liners and mill shell using the energy balances in order to model
energy loss from the mill. The energy loss via convection through the mill shell is
accounted for by quantifying the overall heat transfer coefficient of the shell.
Batch tests with balls only were conducted. The practical aspect of the work
involved the measurement of the temperatures of the mill load, air above the load,
the liners, mill shell and the environmental temperature. Other measurements
were: mill power and sound energy from the mill. Energy balances are performed
around the entire mill.
A model that can predict the overall heat transfer coefficient over a broad range of
operating conditions was obtained. It was found that the overall heat transfer
coefficient for the grinding mill is a function of the individual heat transfer
coefficients inside the mill and outside the mill shell as well as the design of the
liners and shell. It was also found that inside heat transfer coefficients are affected
by the load volume and mill speed. The external heat transfer coefficient is
affected by the speed of the mill. The values for the overall heat transfer
coefficient obtained in this work ranged from 14.4 – 21W/m2K.
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List of Publications
The author has published the following papers based on the contents of this
dissertation as follows:
Published conference abstract
Kapakyulu, E., and Moys, M.H., 2005. Modelling of energy loss to the
environment from the grinding mill, Proceedings of the Mineral Processing 2005’
Conference, SAIMM, Cape Town, South Africa, 4-5 Aug. pp 65-66 - SP03
Research Papers: Accepted for publication and currently in press in Minerals
Engineering:
Kapakyulu, E., and Moys, M.H., 2006. Modelling of energy loss to the
environment from a grinding mill, Part I: Motivation, Literature Survey and Pilot
Plant Measurements, (Currently in press in Minerals Engineering)
Kapakyulu, E., and Moys, M.H., 2006. Modelling of energy loss to the
environment from a grinding mill, Part II: Modeling the overall heat transfer
coefficient, (Currently in press in Minerals Engineering)
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