India’s power demand is largely met by coal-based generation plants. Therefore, to ensure continuous power supply, it is important to undertake operations and maintenance (O&M) for these plants, and even more so considering the mounting demand for power and the increasing integration of alternative sources of energy into the grid.
However, the country’s changing power scenario requires coal-based plants to modify their O&M practices. For ins-tance, complete closed-cycle cooling water systems can be installed in new and existing coal-based plants to lower their environmental impact, while hybrid cooling towers can be installed to lower the water consumption.
Another key requirement is flexibility. Due to the increasing renewable energy integration, plant operation has become more challenging. This has also changed the demand pattern in the grid, which requires coal-based plants to respond quickly to the rapid alterations at the regional load dispatch
centres. This, coupled with tighter environmental and emission norms, makes maintenance even more important. Control systems also need to be tuned to run the plant smoothly.
The increased use of washed coal can also improve plant operations. Also, the use of upgraded materials in key equipment such as boilers will help withstand the stress of cyclic loading. Meanwhile, the firing system needs to be kept at optimum levels to enable faster start-up as required by varying load at the grid. Since coal-based generation is used primarily for meeting the base power demand, reliability is of prime importance in these plants.
Moreover, the plant load factor (PLF) of coal-based plants has been constantly falling with the alternative sources of power gaining mainstream status, thus reducing the demand for coal-based generation at the grid. As a result, the plants have to run at reduced efficiency, which increases their wear and tear, downtime and maintenance requirements.
Coal-based plants are becoming inc-reasingly sophisticated with optimisation being an important consideration for their successful operation. It is achieved through the successful monitoring of key performance indicators along with a comparative analysis of their historical data. The heat rate deviation from specified norms and its quantification in terms of monetary losses help understand the current operating procedures and requirements of the system. This is followed by a detailed analysis and discussion to resolve the problem.
Outages are also a key parameter for determining the health of a coal plant. These are analysed thoroughly and the reports shared with the concerned personnel along with recommendations to reduce such occurrences in the future. In addition, technical compliance directives are issued across the organisation along with detailed location management instructions for each power plant.
As part of the operational best practices, cycle chemistry parameters are adhered to and any deviations are immediately corrected. Meanwhile, constant monitoring helps avoid delays in system shutdown in case of emergencies such as a condenser tube leakage in the cooling water system. In addition to these, plant operations need to comply with the specified environmental norms that require replacement and retrofitting of environment protection devices as well as measures to reduce water consumption.
Personnel safety training and interlock protection systems are also essential for smooth operations of the plant. The proper use of personnel protection devices including following emergency instructions results in fewer accidents. In addition, permit-to-work is necessary for all the equipment. Further, start-up and planned shutdown procedures must be followed without any deviations. Start-up of the system can be done through auto loops and load raising via ATRS (automatic turbine run-up system). Smooth plant operations are also ensured through routine monitoring and recording of incidents as well as listing and displaying of emergency procedures in case of grid or total power failure, equipment failure or fire.
Monitoring coal-based power plants is the basic step for their maintenance. A thorough analysis of the equipment provides an insight into any deviations from production parameters that may occur due to faulty operations. Condition monitoring practices prevalent in coal-based plants include vibration analysis of rotary machines, oil analysis of turbines and dissolved gas analysis of generator transformers. In addition, condenser area conditions are monitored through the acoustic leak detection method while noise levels are monitored for boilers. Also, residual life assessment is undertaken for turbine generator and steam generator sets.
The maintenance of coal-based power plants has evolved from preventive and reactive maintenance to predictive maintenance, which involves data collection to determine the health of the equipment and based on that predicts the failure and the need for corrective action. Predictive maintenance analyses the data collected during continuous condition monitoring and helps improve plant availability, arrest performance degradation and optimise the time between two preventive maintenance sessions.
Preventive maintenance of coal-based power plants is a periodic and routine process that improves output. It is done to identify and eliminate recurring failures as well as for the replacement, restoration or repair of the equipment. This type of maintenance is undertaken after studying the historical data gathered from the equipment. Reliability-centred maintenance is also undertaken for coal-based power plants. It analyses failure modes and determines the mix of condition monitoring, and predictive and preventive maintenance.
Overhauling is vital to ensure optimum coal plant operations. For effective overhauling, continuous preparation is required for at least two years in advance and the overhaul preparedness index needs to be monitored. Modern tools are used for the inspection and repair of the equipment and periodic quality checks are carried out to ensure the effectiveness of the overhauling procedure. The right time for plant overhaul is determined on the basis of the condition of the equipment, the Central Electricity Regulatory Commission clearance and grid requirements.
Meanwhile, the need for overhauling is determined based on the generation, heat rate and other performance parameters along with specific oil and auxiliary power consumption patterns. Unexpected equipment breakdown, repetitive need for maintenance and deviation from environmental norms also call for overhauling of the equipment.
Effective O&M practices aim to ensure smooth plant operation and provide flexibility to the plant. Maintenance practices should be categorised as long and short term and carried out as per schedule to avoid unnecessary downtime of the plant. Plant overhaul and maintenance are as essential as deploying new plants and utmost care must be taken while carrying out these procedures. Historical data is an important part of preventive and predictive maintenance, and all records must be made available to the concerned personnel at all times to make the maintenance process successful.
Almost half of the downtime of coal-based power plants is due to poorly executed O&M procedures. Therefore, it is imperative for operators to follow the relevant guidelines to ensure improved availability and performance of coal-based plants. The adoption of advanced technologies will enable plant operators to undertake smart O&M practices. Further, standard operating procedures must be made mandatory at every coal plant to reduce forced outages and ensure uninterrupted power supply. n
Based on a presentation by Sudip Nag, General Manager, Operation Services, NTPC Limited