With the increasing share of renewable energy in the power mix, thermal power plants (TPPs) are required to frequently adjust their operations through load cycling, involving quick ramp-ups and ramp-downs. As India aims to meet 50 per cent of its energy needs from renewables by 2030, it is crucial for TPPs to operate at technical minimum levels despite being designed for baseload operation. This cycling and part-load operation near minimum levels causes thermal stress, component deterioration, poor heat rates and higher auxiliary power consumption, leading to increased operational costs, outages and revenue loss. TPPs also face stricter emission norms, with penalties for non-compliance, necessitating upgrades to pollution
control systems.
To maintain efficient operations, TPPs must adopt effective operations and management (O&M) strategies. This is crucial not only for achieving high performance levels but also for maintaining the health and longevity of the equipment.
Maintenance methodology
Preventive equipment maintenance is crucial to prevent major issues during operation. This includes multiple generator inspection levels: initial inspection (after 10,000 to 20,000 operating hours), minor inspection, intermediate inspection and major inspection (recommended after 40,000 to 60,000 hours). Conducting minor and intermediate inspections between major inspections ensures the generator’s continued reliability and performance.
The stator inspection schedule should include measuring the insulation resistance of the stator winding, implementing insulation and leakage tests on the H2 system and dismantling bushings to replace gaskets. Additionally, the stator end shields should be dismantled, gaskets should be replaced and the condition of seals between the stator core and housing should be checked. Rotor inspection should include performing a runout check, inspecting rotor wedges, retaining rings and bearing surfaces, and measuring insulation resistance. Additionally, the shaft seal contact faces, rotor alignment and coupling flanges should be checked.
To boost boiler efficiency, reducing flue gas temperature by 22 °C can increase efficiency by 1 per cent and raising combustion air temperature by 20 °C can improve thermal efficiency by 1 per cent. Cutting excess air by 5 per cent can also enhance efficiency by 1 per cent. Additionally, to prevent heat loss, regular insulation surveys should be conducted using a pyrometer.
Condition monitoring of equipment should include conducting vibration analysis for equipment rated at 45 kW or higher and performing debris analysis on critical components such as boiler feed pumps, mills and primary air fans. Further, thermography of outdoor electrical equipment, boiler insulation and ducting should be considered. Electrostatic liquid cleaners should be employed for high pressure and low pressure bypass systems to enhance equipment reliability and efficiency.
Predictive maintenance uses online condition monitoring to forecast equipment failures. Advanced pattern recognition (APR) systems analyse historical equipment behaviour to develop a series of operational profiles. These profiles are continuously compared with real-time data, enabling the system to detect deviations well before they trigger distributed control system alarm limits. APR systems are not limited to monitoring a single parameter but use a sophisticated algorithm that considers multiple factors. By providing early warnings of incipient failure modes, APR-based systems support continuous monitoring of equipment health and performance. This proactive approach allows experts to identify subtle changes in equipment behaviour, minimise operational risks and optimise maintenance strategies. Additionally, these systems facilitate informed decision-making by providing timely insights into potential issues, thereby enhancing the reliability and efficiency of operations.
Utilities are increasingly adopting reliability-centred maintenance (RCM) strategies to improve the dependability of power plants. RCM focuses on assessing the risk and cost associated with maintaining specific equipment, allowing for the prioritisation of maintenance activities more effectively. This approach combines preventive, predictive, real-time, reactive and proactive maintenance techniques to optimise equipment availability while reducing maintenance expenses. By emphasising reliability over mere availability, RCM takes a proactive stance, aiming to prevent failures before they occur rather than simply responding to them. Through the use of real-time data for analytics and predictions, engineers can identify opportunities for enhancing reliability and receive automatic alerts when equipment health declines beyond acceptable limits.
Further, utilities can develop a strong maintenance strategy by conducting root cause analysis on various equipment, considering generation loss and mean time before breakdown. Failure modes and effects analysis should be performed based on the severity, frequency, detection rating and financial impact of failures. For critical equipment and operations, a zero-forced-outage plan is essential. Monitoring the overhauling readiness and quality indices is also crucial.
Standard operating procedures
A daily heat rate deviation report should be generated, which tracks key parameters such as main steam pressure and temperature, reheat steam temperature, superheater and reheater spray flow, and condenser vacuum. For combustion optimisation, key operational practices include cross-checking the air preheater (APH) intake for oxygen and carbon monoxide with a portable gas analyser and monitoring APH and duct in-leakage. Additionally, oxygen levels in flue gas, unburnt carbon in fly ash and bottom ash, feed water temperature at the economiser inlet, make-up water flow and auxiliary power consumption should be monitored closely. These metrics can be regularly compared with historical data from the unit and other similar auxiliaries to identify and manage controllable factors that impact plant energy efficiency. Moreover, an insulation survey should be conducted whenever feasible to further enhance efficiency.
Additionally, optimising cooling tower fans, cleaning condenser tubes and regularly checking the terminal temperature differential of heaters are essential. Helium gas testing can detect air ingress into the condenser and radiation loss can be minimised by conducting insulation studies on critical pipes and the furnace area.
Further, monthly (and as needed) efficiency and performance tasks should include conducting efficiency tests for each unit, performance tests using special instruments ( for instance, clean air and dirty air flow tests), and testing the performance of the condenser, airpreheater and high pressure heaters. Additionally, fire fighting mock drills can be carried out.
Emerging solutions
The digitalisation and integration of advanced analytics provide a valuable opportunity to enhance the accuracy of generation scheduling and optimise coal stock management. This approach enables more effective planning and scheduling of coal deliveries, ensuring that resources are used efficiently and downtime is minimised, aligning with the actual operational demands of the thermal plant. Drones can be employed to measure coal heap volumes and inspect bunkers, while robotics can detect silting in underwater pipes. Thermal imaging of coal yards can also be utilised to reduce heat loss.
Gamma rays are increasingly being used to monitor emissions, assess electrostatic precipitator hopper emptiness and schedule maintenance. Exfoliation meters track oxide layer deposits in coils, while small oil igniting systems and phased array ultrasonic tests identify metallurgical flaws. An oxygenated treatment cycle can reduce corrosion and iron carryover.
Other emerging O&M practices include furnace mapping for boiler combustion optimisation, equipment changeover scheduling via SAP, cross-checking air preheater intake with portable gas analysers, and utilising boiler tube leakage management, smart soot blowing and insulation surveys for critical piping and furnaces.
To enhance water efficiency, plants should implement air-cooled condensers, particularly in water-scarce regions, as they reduce cooling water demand by using dry cooling to condense steam. Increasing cycles of concentration (CoCs) in cooling systems is also essential, as it minimises blowdown and makeup water requirements. While many systems operate with two to four CoCs, achieving six or more is possible. Additionally, TPPs are moving towards zero liquid discharge by using advanced wastewater treatment technologies to purify, recycle and reuse wastewater, effectively closing the water loop within the plant.
Conclusion
Effective O&M methods are vital in the coal-based power sector, especially given shifting fuel mixes, flexible operations and stringent environmental and safety standards. Adopting advanced O&M strategies and digital solutions will be key to ensuring sustainable operations and high performance in the future. It is crucial to adopt strategies that emphasise maximum mechanisation with minimal manual work. Examples of mechanisation include electric impact wrenches, electrically powered 2T gantry cranes, electric-operated rotor stands, portable plasma cutting machines, battery-operated pick-and-carry cranes and Teflon wheel-mounted fabricated trolleys. Utilities should focus on improving key operational areas while outsourcing less critical functions to business partners who meet strict performance standards. Effective inventory management can be achieved through vendor-managed
inventories and annual rate contracts for fast-moving items.
There should be a sustained focus on integrating new and innovative technologies, implementing cost-saving measures and automating work processes. Capacity building and training, including the use of augmented reality and hands-on maintenance, are essential for improving O&M practices at TPPs. A comprehensive techno-economic analysis is necessary to determine the most suitable technologies and solutions, balancing significant capital expenditures with minor modifications. By prioritising these strategies, power plant operators can enhance efficiency, reduce costs and ensure the long-term sustainability and reliability of their operations.
