Over the years, the power stations have been witnessing deterioration in their performance as they age. This is accelerated if proper operations and maintenance (O&M) practices are not followed. Good O&M practices at thermal power plants (TPPs) have significance not only in terms of achieving high levels of performance, but also in ensuring the health of the equipment at power stations. This requires multiple interventions in terms of the workforce, technology, processes and infrastructure. The uptake of O&M also stems from the need to reduce the cost of generation and increase efficiency.
New and emerging requirements
Due to the growing renewable energy penetration, TPPs are undergoing multiple rounds of load cycling, and require quick ramp-up and ramp-down capabilities. Power plants are witnessing an increase in creep-related failure due to pressure and temperature cycling. Flexibilisation requires utilities to run the thermal units at technical minimum load. This can lead to an unstable furnace during low load operation and increase the secondary heat rate and cost of power generation, while also increasing the secondary oil consumption for frequent reserve shutdown.
Apart from this, stringent emission norms for sulphur oxides (SOx) and nitrogen oxides (NOx) have led to a high capex requirement for the installation of flue gas desulphurisation (FGD), selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR), besides increasing the opex, which has further increased the cost of generation from TPPs. In view of the changing landscape and challenges faced by TPPs, such as changing fuel mix, flexible operations and tighter environment norms, adopting efficient O&M strategies has become crucial to ensure uninterrupted operations.
O&M best practices
With the integration of renewables, most TPPs have started operating at minimum technical load. As a result, the secondary air damper control tool is gaining prominence for getting the best mill combination and maintaining an optimum boiler temperature. To monitor emission levels, gamma rays can be used as they help to check electrostatic precipitator hopper emptiness and plan maintenance accordingly. Exfoliation meters are also gaining traction. They are used to check the oxide layer deposition in FSH and FRH coils. To check the boiler combustion and control the furnace exit temperature, furnace mapping can be carried out. Further, the adoption of equipment changeover tools can help schedule changeover as per SAP and maintain equipment health. The daily monitoring of boiler metal temperature excursions can be carried out through an X-tool, while the mill PF pipe velocity balance can be assessed through DAVT. Smart soot blowing is also gaining traction for effective soot blowing.
Other operational practices include cross-checking of the air pre-heater (APH) inlet for oxygen and carbon monoxide with a potable gas analyser for combustion optimisation as well as APH and duct in-leakage monitoring. Heat rate is a critical parameter of power plants that directly reflects company profitability. High energy drain valve passing leads to heat rate deterioration. Thus, there is a need to regularly monitor high energy drain valve passing. The optimisation of cooling tower fans and cleaning of condenser tubes should also be undertaken. Further, utilities should monitor the terminal temperature difference of heaters at regular intervals. Helium gas testing can be helpful in detecting air ingress into the condenser. In addition, an insulation survey of critical piping and furnace area can be used to reduce the radiation loss.
A strong maintenance strategy is one that is devised by utilities based on the root cause analysis for different classes of equipment, generation loss and mean time before failure. A failure modes and effects analysis (FMEA) of equipment should be undertaken based on the severity, frequency, detection rating and cost impact of the failure. The zero forced outage strategy should be implemented for critical equipment and processes. The overhauling preparedness index and the overhauling quality index should be monitored. Other maintenance practices include boiler tube leakage control, and modular replacement of sub-assembly and main assembly to reduce the maintenance downtime. Besides this, a preventive maintenance schedule must be followed as per the equipment classification category and strong condition-based maintenance must be adopted.
New and innovative technologies are also gaining popularity for efficient O&M. These include the introduction of a mini oil ignition system, and a phased array ultrasonic test for the detection of metallurgical defects. Robotics can be used for the detection of silting in underwater pipes, while drones can be used to measure the volume of coal piles and for bunker inspection. Further, thermal imaging of coal yards can be undertaken to reduce the heat loss. Meanwhile, a cycle chemistry programme using oxygenated treatment can reduce the corrosion and iron carryover. In addition, cycle chemistry guidelines should be put in place for start-up and flushing, and cycle chemistry instrumentation should be adopted as per the International Association for the Properties of Water and Steam. Further, an approach towards maximum mechanisation with minimum manual work strategy can be adopted for smooth operations. Mechanisation can be brought about through the adoption of an electric impact wrench, electrically operated 2T gantry cranes, electric operated rotor stands, portable plasma cutting machines, battery-operated pick and carry cranes or Teflon wheel-mounted fabricated trolleys.
At the fuel level, some of the key practices are pile age monitoring, which is useful to reduce heat loss and maximise heat value utilisation. The coal blending strategy should be adopted to utilise the fuel in the most efficient and cost-effective manner. Selective bunkering helps in the utilisation of low calorific value coal during technical minimum loading. A strategic inventory plan should be devised to reduce the accumulation of inventory.
Data analytics, machine learning and artificial intelligence can also offer several benefits. The implementation of data analytics to track the operating parameters for reliable operation can help in the early detection of excursions or defects. Data analytics can assist in the improvement of cyclic efficiency through the detection of energy loss online, and suggest corrective actions. It can also help optimise the maintenance strategy by restricting unscheduled outages and eliminating unnecessary preventive maintenance. Equipment health monitoring can also be undertaken through real-time monitoring of critical parameters deviations and condition monitoring.
The utilities should focus and strengthen critical operating areas, while non-critical areas should be outsourced to business partners that follow strict KPI monitoring. Inventory management through vendor-managed inventory and an annual rate contract for fast-moving items should be adopted.
Conclusion
To achieve business excellence, utilities should implement best-in-class O&M processes for business sustainability. Activity-based budgeting and implementation of cost-saving initiatives along with optimum fuel blending are needed to maintain a low cost of generation. Strategic initiatives include the implementation of new technologies and focus on innovation, automation and mechanised work to reduce manpower requirement. The key maintenance processes can include root-cause analysis, FMEA, reliability-centred maintenance, multi-year overhaul plan, zero forced outage strategy, and systematic inventory management. To achieve operational excellence, and maximise plant availability and load factor, utilities should have a plant performance improvement suite and work towards reducing the start-up time.
Overall, there should be continued focus on the adoption of new and innovative technologies, cost saving and mechanisation of work. Capacity building and training through augmented reality and practical maintenance work could go a long way in improving O&M at TPPs.