OPERATIONS
A well-established deep level mine can have virgin rock temperatures of between 50 0 C and 60 0 C.
Water is used as a cooling medium in cooling systems and
it absorbs heat in the liquid phase (heat exchanges), rises in
temperature and then disposes of the heat by evaporation
(cooling tower) and drops in temperature. The water itself does
not cause any problems; but being the universal solvent, it
harbours several unwanted guests. These contaminants may be
brought in with the municipal water supply or scrubbed out of the
air stream used to assist evaporation. Depending on the material
of construction of the cooling tower the water-quality control
limits indicate the limit the cooling tower can run at before scale
and corrosion start forming on the heat-transfer surfaces.
The satisfactory performance of cooling equipment is
dependent on correct selection and proper attention to overall
system design, installation, water care and maintenance.
“Our water-treatment programmes include automatically
controlled dosing of chemicals and the bleed-off system. The
cycles of concentration are optimised to minimise water loss
through bleed-off while controlling corrosion and scaling,”
Myburgh says.
The selection of a model is based on a thermal duty and the
wet-bulb temperature. Thermal ratings are based on the wet-
bulb temperature of the air entering the equipment and do
not consider any recirculation of warm and humid discharge air
which may occur under certain weather and wind conditions.
Verification of ratings assumes a test according to a recognised
test standard and the application of tolerances as recorded
during the test and applied to the test results.
The fluid to be cooled must be compatible with the coil material.
Fluids not compatible with coil materials can lead to corrosion
and tube failure. Certain fluids may require occasional pressure
cleaning or mechanical cleaning of the inside of coil tubes. In
such cases the coil must be designed to provide this capability.
www. africanmining.co.za
African Mining Publication
African Mining
African Mining April 2020
27