Abstract
M.Ing.
The dissertation is an investigation on the implementation of new technologies (five off) in a
coal pulverising with main aim to optimise mill maintenance interventions. The technologies
in question are:
• Stationary air throat replaced with a rotating throat assembly.
• Hydro-pneumatic mill loading cylinders replaced with airbags.
• Classifier cone modification.
• Introduction of triton material for the mill spider guide plates.
• High chrome mill grinding balls.
Every maintenance intervention, even if planned, negatively affects a plant’s availability and
reliability. A Babcock and Wilcox (B&W) at Kriel power station (ESKOM) was used for the
testing of the mentioned technologies. The mill model/size is a B&W 10.8E mill. The aim of
the introduction of new technology on a mill is to optimise the period between required
maintenance activities. A higher availability will assist in achieving good plant maintenance
performance indicators. It needs to be noted that the dissertation focussed on the financial
and technical parameters of a specific modification. This in an effort to increase uptime and
reduce costs as part of a business drive for bigger profit margins.
The new technologies tested were thus evaluated from a technical and financial point of
view. Each technology was implemented at different time periods and nowhere was any
tests performed in parallel on a single mill. To get approval from an investment committee for
release of money for tests/modifications, technical and financial assumptions need to be
made regarding the performance parameters of the modification/change. Once a
modification is being tested, actual plant data can be used as inputs into the execution
phase of the modification as assumptions can be replaced with test data. A financial model
was developed to “test” the financial feasibility of the proposed changes/modifications.
With new technology successful implemented in the plant the current maintenance strategies
for maintenance interventions can be re-evaluated as the proposed modifications removed
historic barriers that determined the current used based maintenance intervals. An example
is where a mill is taken from service to replace or repair the stationary air throat (typically
every 5 000 operating hours). With the newly applied technology (rotating throat
assemblies), there is no need for maintenance interventions every 5 000hrs as a rotating
throat assembly can run without major interventions for 60 000hrs.