Abstract
Coal pulverizing mills are very crucial equipments of any thermal power plant. They
pulverize the coal that is burned in furnaces to release the heat energy that is required in
the power boilers. Pulverized coal burns more efficiently and releases more heat energy
compared to un‐pulverized coal. The coal gets fed into the mill as an input simultaneously
with the heated primary air, the primary air performs two critical functions in the
process, it dries the coal and it acts as a transportation medium for the pulverized coal to
the combustion chamber for the ease of burning.
There are different types of mills that are available, however, the purpose of this research
work only the Vertical Spindle Mills (ball and ring) type and Vertical Spindle Mills roller
type have been considered because the power station for whose reliability management
is under study only uses these two types.
Reliability management in terms of maintainability of the mills is crucial since the mills
are a critical part of the plant; every boiler is normally fitted with one extra mill which is
normally kept as redundant for reliability purposes, in this way there is always a standby
mill to enable the unit to always operate at full capacity to reliably maintain the full load
unit output all the time.
There are reliability strategies that are employed to ensure that the plant is always
available when required and to avoid unexpected breakdowns, Reliability Centred
Maintenance is an optimum combination of reactive, interval‐based, condition‐based,
and proactive maintenance practices, it is a comprehensive maintenance strategy that
carters for the holistic view of maintainability and reliability of the plant from the
preventative to the corrective perspective of maintenance based on the requirements and
criticality. The Failure Mode Effect and Criticality Analysis (FMECA) is used to detect a
number of failure modes, reasons for failures, effects of failure and the level of criticality
of each failure to the coal pulverizing mill and production, these analyses help to develop
an informed Reliability Centred Maintenance (RCM).
Total Productive Maintenance is a type of maintenance strategy that is based on the
concept of Total Quality Management attitude of zero defects; it is basically built on the
idea of five fundamentals which are the improvement of equipment effectiveness, self-sufficient maintenance, training of all staff, execution of planned maintenance and
achievement of early equipment management.
Through the FMECA methodology the critical parts of the mills are identified, all of them
are assigned different and fitting maintenance strategies, some of them are maintained
based on time intervals measured in running hours, some in time intervals based on time
blocks regardless of running hours and some based on their conditions after inspections.
There are also components that are considered not to be critical, those are usually left to
run to failure and get repaired or replaced when they fail.
The strategies in place are effectively implemented with the full involvement of
operations, maintenance and management. The teams are adequately trained to gain a
level of competence that is required in the mills. There are PMs and check sheets in place
to assist the teams to effectively execute the required tasks, at the required time.
Keywords:
Mills, Reliability Centered Maintenance, Maintenance strategies, and Failure Mode Effect
and Criticality Analysis .