By Prakash Sharma, Chief, O&M, Prayagraj Power Generation Company Limited, Tata Power
The operating context for thermal power plants (TPPs) has evolved significantly in recent years. Variations in coal quality, higher ash content, tightened emission norms and sustained pressure on operating costs have elevated the importance of disciplined operations and robust maintenance practices. Any disruption in coal receipt, conveying, bunkering or ash evacuation directly affects unit availability, auxiliary power consumption and overall plant reliability. Consequently, coal handling plants (CHPs) and ash handling plants (AHPs) can no longer be treated as peripheral systems but must be managed as reliability-critical assets within the overall operations and maintenance (O&M) framework.
Advancing maintenance maturity: From preventive routines to reliability-centred O&M
In coal handling and ash handling systems, equipment failures rarely occur without warning. However, when maintenance practices remain reactive or calendar-driven, early signs of degradation often go unnoticed, leading to forced outages, safety incidents and higher life cycle costs. Therefore, improving the reliability of these balance-of-plant systems depends less on increasing maintenance effort and more on advancing maintenance maturity.
Maintenance practices typically evolve through four stages – corrective maintenance, preventive maintenance, condition-based maintenance and reliability-centred maintenance. In corrective maintenance, intervention occurs only after failure, resulting in significant disruption and high safety exposure. Preventive maintenance introduces scheduled activities based on time or operating hours but often fails to account for the actual condition of the equipment. Condition-based maintenance marks a shift towards monitoring asset health using diagnostic indicators, while reliability-centred maintenance integrates condition monitoring with root cause analysis, failure mode and effects analysis and system-level understanding to optimise both reliability and cost.
A key distinction in this evolution is between availability and reliability. Two systems may demonstrate similar availability yet behave very differently in operation. A reliable system delivers consistent performance with fewer deviations, fewer forced interruptions and greater predictability, enabling better planning of manpower, spares and outages. In material handling systems, this distinction is critical as frequent short-duration disruptions may go unrecorded as outages but still erode performance and efficiency.
Within CHP operations, maintenance maturity is strengthened through proactive planning and structured condition monitoring. Critical equipment is monitored using oil analysis, vibration analysis and motor current signature analysis to detect early-stage faults. Conveyor belts and idlers are subject to routine health assessments, supported by in-house idler repair capabilities to reduce downtime. Periodic inspections of conveyor pulley bearing clearances are carried out to identify progressive wear before it results in failure.
These practices are complemented by structured diagnostics and follow-up actions.
As maintenance practices mature, data from condition monitoring and operational performance is increasingly used to support reliability-centred maintenance decisions. This enables the prioritisation of interventions based on risk and impact rather than fixed schedules, reduces unnecessary maintenance, and improves overall system stability. For CHP and AHP systems that operate continuously under variable loads and material conditions, such maintenance maturity forms the foundation for sustained reliability and safer operations.
Improving efficiency through auxiliary power consumption control
In TPPs, auxiliary power consumption (APC) is often treated as a reporting parameter rather than an operational performance indicator. In practice, however, APC trends reflect the effectiveness of O&M discipline across material handling systems. Inefficiencies such as idle running, partial loading, frequent start stop cycles and degraded equipment condition manifest directly as higher auxiliary consumption in both coal and ash handling plants.
Within a coal handling plant, APC control begins with systematic monitoring. Equipment-wise auxiliary power consumption is tracked on a continuous basis, and time-series analysis is used to identify abnormal deviations and energy loss pockets. This approach enables the detection of inefficiencies that may not trigger alarms or immediate failures but steadily erode performance, such as conveyors running without load or operating outside optimal loading ranges. By linking APC data with operating practices, corrective action can be taken promptly, including changes in conveyor operation, bunkering sequence or maintenance intervention.
Operational discipline plays a central role in CHP energy efficiency. Operational discipline also extends to coal yard management for stacking and reclaiming, which plays an important role in maintaining fuel consistency before bunkering. Grade-wise and source-wise stacking, along with planned reclaiming in a controlled sequence, support more uniform gross calorific value (GCV) feeding to bunkers and help reduce downstream operational variability. In addition, effective fire prevention and detection systems in the coal yard are essential for safe and reliable CHP operations. Avoiding idle conveyor running, maintaining belt loading within the optimal range of 70-85 per cent and minimising frequent start-stop cycles help reduce unnecessary power draw and mechanical stress. Defined operating sequences during bunkering further limit idle operation and stabilise energy consumption. Over time, these practices translate into measurable reductions in CHP auxiliary power consumption.
A similar data-driven approach is applied in AHPs. APC is monitored daily with equipment-wise segregation to capture the energy profile of individual systems. Comparative assessments across operating dates are used to quantify variations and identify performance deterioration.
Insights from APC monitoring are integrated with maintenance and operational decision-making. Elevated consumption levels often signal emerging equipment issues, suboptimal operating modes or deviations from standard procedures. Addressing these signals early helps prevent escalation into reliability problems while also improving overall plant efficiency. By treating auxiliary power consumption as an outcome of O&M performance rather than as a standalone number, CHP and AHP operations can be aligned more closely with both cost control and reliability objectives.
Strengthening ash handling reliability and asset life
In coal-based TPPs, ash handling systems operate continuously and any disruption can quickly escalate into boiler instability, deration or forced outages. As ash generation increases under high-ash coal regimes, disciplined O&M practices in AHPs become essential to protect generation continuity, control auxiliary power consumption and meet environmental requirements.
Bottom ash evacuation is managed through clearly defined operating routines. Bottom ash hoppers, including economiser and water-impounded hoppers, are de-ashed once per shift under normal conditions. Maintained-mode evacuation is followed to prevent refractory damage and maintain stable flame conditions in the boiler. Completion of de-ashing is confirmed through a visual inspection of discharge quality and evacuation duration. During periods of high ash content or clinkering, de-ashing frequency is increased to twice per shift to prevent accumulation and operational stress.
Dry ash handling reliability is supported through vacuum-cum-dense phase conveying systems. In this arrangement, ash from electrostatic precipitators and air preheater hoppers is evacuated via vacuum systems beyond buffer hoppers into intermediate silos, followed by dense phase transfer. Stable operation is ensured by maintaining the system within the designed operating envelope, including appropriate vacuum levels and dense phase conveying pressures, thereby reducing choking, line wear and unplanned interruptions.
Preventive and condition-based maintenance practices form the backbone of AHP reliability. Strict adherence to preventive maintenance schedules is maintained, with original equipment manufacturer visits planned at defined intervals. Maintenance kits are deployed based on operating hours and service life, supported by periodic oil analysis, vibration analysis, pipe thickness measurements and motor signature analysis. These diagnostics help identify early-stage degradation and enable timely intervention.
Targeted material upgrades are implemented to extend equipment life and reduce leakage-related risks.
Safety and environmental controls are integrated into routine AHP operations.
Conclusion
O&M excellence in coal-based TPPs increasingly depends on the reliability of balance-of-plant systems. The practices outlined across coal and ash handling operations demonstrate that improvements in safety, reliability and efficiency are achieved through disciplined operating routines, maintenance maturity and data-driven performance monitoring.