A dissertation submitted to the Faculty of Engineering,
University of the Witwatersrand, Johannesburg, for the
Degree of Master of Science. / Storage and waste dumps from coal mining tend to
spontaneously combust. This is mainly as a result of the
oxidation process which is accelerated by the
availability of oxygen and the exothermic nature of the
oxidation process. In cases of poor ventilation the heat
accumulation within the bed is thought to lead to the
spontaneous combustion of coal.
The work in this dissertation aims to investigate the
change in oxygen concentration in a bed of coal and also
measure the rate of oxidation (oxygen absorption) in a
closed reactor under isothermal conditions. Drying rate
of coal under nitrogen was also looked into.
An analysis of the oxygen concentration profile in a
three metre 20 cm ID plastic column filled up with coal
has been carried out. As the coal ages (becomes oxidised)
its reactivity towards oxygen decreases and changes in
the oxygen concentration profile are noticed.
Experiments have been carried out up to 8 months and from
the results obtained, a simple pseudo-steady-state model
has been developed to describe the diffusion of oxygen
into a reacting coal bed. The findings could prove useful
in trying to find a solution to coal and waste dump fire control.
The second experiment is a simple isothermal oxygen
absorption experiment in which the rate of absorption of
oxygen on a given coal sample is measured at different
initial concentrations of oxygen. The initial
concentration of oxygen is varied over a fairly wide
range in order to determine the dependence of the rate of
oxidation on the oxygen concentration. The rate- limiting
step in low temperature oxidation of coal is found to be
the absorption of oxygen.
Moisture also plays a role in coal oxidation. Drying
experiments were also carried out so as to quantify and
investigate the rate of loss of moisture. Models have
been developed which try to explain tile mechanisms
involved in the drying process. The modelling suggest
that the bound water model is more appropriate to the
type of behaviour exhibited during the drying process. / Andrew Chakane 2018
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/25891 |
| Date | January 1998 |
| Creators | Kaitano, Rufaro. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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