The R&M programme for thermal power plants (TPPs) has been in place for over 35 years now. The R&M of thermal power generating units is undertaken for operating units well equipped with modified and augmented systems. This is done with a view to improve their operating performance, reliability and availability to the original design values as well as to reduce maintenance requirements. There are many drivers for the R&M of TPPs, that are not covered under the regular plant operations and maintenance (O&M).
These include generation sustainability and the need to overcome problems that arise due to generic defects, design deficiencies, inefficient operation, non-availability of spares due to obsolescence of components, deterioration in the quality of coal as compared to the design coal, and equipment replacements on account of unforeseen failures.
In recent years, R&M practices are being undertaken to not only help enhance efficiency but also to meet the emission norms and achieve flexibility in generation. With stringent environmental norms in place for water consumption and particulate matter (PM), SO, NOx and mercury emissions, R&M practices are being widely adopted to reduce the environmental impact of TPPs, making it easier to adapt to the changing energy scenario.
Further, as the power system incorporates more renewable energy, flexibility of TPPs is becoming a key requirement. While many power plants operating on supercritical technology offer flexibility in operations, older power plants experience a severe deterioration in performance under flexible operations. Various R&M measures can help in improving flexibility. These include the installation of advanced burners and indirect firing systems in boilers, wherein special alloys are used for improving material strength, reducing mill size, and increasing the number of mills.
Progress so far
A total of 653 units, with an aggregate capacity of over 81 GW, have undergone R&M/life extension (LE) works since 1985. During 2012-17, R&M/LE works were carried out at 7,200 MW of units as compared to 17,000 MW during 2007-12.
The Central Electricity Authority (CEA) has identified 71 units with an aggregate capacity of 14,929 MW for R&M/LE works for the period 2017-22. For LE works, a total of 34 units (aggregating 7,570 MW) have been identified (in the state sector) and for R&M works, 30 units (7,135 MW) have been identified in the state sector and seven units (224 MW) in the central sector. Up to December 2021, a total of six units comprising a capacity of 887 MW underwent R&M/LE works under the programme. These included units owned by NEEPCO (Kathalguri CCGT), Gujarat State Electricity Corporation Limited (GSECL) (Ukai and Wankabori stations), Mahagenco (Koradi station) and Uttar Pradesh Rajya Vidyut Utpadan Nigam (Obra station).
The Ministry of Environment, Forest and Climate Change (MoEFCC) notified and revised the norms for TPP emissions in December 2015. In order to meet these norms, power plants are required to install/retrofit various technology solutions such as selective non-catalytic reduction and selective catalytic reduction systems, electrostatic precipitators (ESPs), and flue gas desulphurisation (FGD) systems. FGD systems are planned to be installed for around 168.9 GW of capacity for SOx control. As of February 2021, FGDs have been commissioned in six thermal units, totalling 2,160 MW of capacity.
Similarly, ESPs, which help in controlling PM emissions, are to be installed in 220 units, totalling 63.4 GW. Although most of the power plants have already installed ESPs since Indian coal has a high ash content and leads to significant generation of PM, there are concerns over their efficacy and operational performance, which means that upgraded systems could be required for the existing projects.
R&M for flexibilisation of TPPs is another key emerging application of the R&M programme. With increasing penetration of renewable energy, maintaining grid stability and security has become challenging. Undertaking R&M of the existing pollution control equipment can help reduce emission levels. With an anticipated renewable energy capacity of 175 GW, the government is targeting to adapt 60 per cent of the installed fleet of TPPs to operate at 55 per cent minimum technical load (MTL). The Ministry of Power has set targets for achieving flexibility (55 per cent MTL) of TPPs (coal/lignite) in a time-bound manner. The targets are 20 per cent, 30 per cent, 40 per cent, 50 per cent and 60 per cent of the total fleet compliant with 55 per cent MTL from 2020 to 2024.
Power equipment major Bharat Heavy Electricals Limited (BHEL) has conducted flexible operation pilot tests at NTPC’s Mauda TPS and West Bengal Power Development Corporation Limited’s (WBPDCL) Sagardighi TPS. Another flexible operation study has been organised by the CEA and implemented by BHEL at GSECL’s Ukai thermal power station Unit 6 (500 MW) on March 4, 2020. A minimum load of 40 per cent with a ramp rate of 3 per cent was achieved as part of the study.
Challenges and the way forward
Notably, R&M is not a substitute for regular annual or capital maintenance, which forms a part of O&M activity. Moreover, middle-life R&M comes up preferably after 100,000 hours of operation.
In terms of a cost-benefit analysis, the decision to invest in R&M/LE&U should be driven by an economic sensitivity analysis of the cost of generation. The benefits are increased efficiency, reduced auxiliary power consumption and fuel consumption, a higher plant load factor (which includes additional generation and availability, and reduced forced outages), and improvement in plant safety and environmental upgradation.
However, the pace of implementation of R&M/LE projects has been rather slow in recent years. Many projects have been facing delays in execution – from conducting feasibility studies to tendering and awarding contracts, procuring materials and commissioning. Often, new defects and damaged equipment are discovered upon opening a plant for R&M/LE, requiring additional materials, which can exacerbate time delays and increase costs. At times, the contract documents fail to address technical issues. The need for shutting down generating units for six to eight months is another key reason for the slow uptake of R&M. Many utilities are not willing to shut down units because of the loss of revenue. Obtaining regulatory clearances for plant shutdowns in order to conduct R&M works is also a time-consuming process. The lack of specialised entities for conducting residual life assessment (RLA) studies of power plants is another big challenge. It is also not easy to define the scope of work and guarantees during such a process. Some old plants, for instance the Singrauli STPS, Talcher TPS and Ramagundam STPS have already undergone R&M and have performed well despite having completed their designed economic life.
Although TPPs have immense potential for R&M, it is important to minimise the time lag between the technical studies and the actual award of contracts and commencement of R&M works for achieving the desired results. Further, adequate regulatory support is imperative for promoting R&M activities.
With a large fleet of TPPs that is more than 25 years old, there is ample scope for performance improvement through R&M in the Indian power sector.