India has set a target to augment its non-fossil fuel electric capacity to 500 GW by 2030. While this is expected to lower its carbon emissions and help meet the growing energy demand, the integration of renewables into the grid will be a major challenge. Such a large renewable energy base is expected to lead to sharp variations in generation. To ensure the security and reliability of power supply and stability of electricity grids while maximising power from renewable energy sources, flexibilisation of existing coal-based thermal power plants (TPPs) is needed.
In this regard, the Central Electricity Authority (CEA) has notified the draft Flexible Operation of TPPs Regulations, 2022. Some of the salient features of the draft are a technical minimum load of 55 per cent for all TPPs; 40 per cent minimum power level (MPL) to support must-run status; a ramp rate of 3 per cent per minute for all TPPs; and a minimum rate of loading or unloading of 5 per cent per minute for supercritical and ultra-super-critical units.
Details of the draft regulations
The regulations will apply to all coal- and lignite-based TPPs and load despatch centres (LDCs). As a general requirement according to the draft, TPPs need to be suitably designed for a full range of ambient and other environmental conditions prevailing at site. The various parts or components or assemblies of equipment and systems need to be of proven materials with established physical and chemical properties. All equipment and systems installed will need to comply with the provisions of statutes, regulations and safety codes, as applicable. The units will be considered for flexible operation throughout their service life. The suitability of units for start/stops and deep load following ramps will be assessed beforehand. The condition assessment of existing plant systems and their upgradation, if required to accommodate the flexible operating requirements, will also be addressed beforehand.
The draft regulation states that for flexible operation, all TPPs will be capable of providing the required output as per the generation schedule finalised by the appropriate LDCs. Based on the availability of must-run stations, plants or units will follow the variable load requirements. The appropriate LDCs will schedule all coal-based TPPs up to the MPL of 55 per cent to support the operation of must-run stations. This needs to be implemented by all TPP units within one year. Further, the appropriate LDCs may schedule all coal-based TPPs, up to the MPL of 40 per cent, to support the operation of must-run stations. The minimum rate of loading or unloading for coal-based TPPs will be 3 per cent per minute above the MPL. For supercritical and ultra-supercritical units, the minimum rate of loading or unloading shall be 5 per cent per minute above the MPL. These measures need to be completed by all TPP units within three years from the date of notification of these regulations, subject to technical feasibility studies to be undertaken in consultation with the concerned original equipment manufacturers (OEMs) or qualified consultants. The TPPs will implement the necessary modifications, if any, to achieve these requirements to generate flexible power according to the schedule finalised by the appropriate LDCs.
The process for the flexibilisation of TPPs will include measures to lower minimum limits of power output, increase ramp rates and optimise the start-up of power plants, which would be implemented based on technical feasibility studies involving the assessment of certain factors in consultation with the concerned OEMs/ qualified consultants. These factors include rated capacity, minimum load design rating with no oil support, design ramp rate, influence of low load operation on components and systems, technical boundary conditions for flexible operation, combustion system optimisation, and coordination of mill and burner systems. TPPs may adopt suitable modifications in consultation with the concerned OEMs/qualified consultants.
Conclusion
The flexible operation of existing TPPs has been identified as a promising measure for balancing the fluctuating renewable power. The draft regulation is expected to pave the way for TPPs to adjust the net power fed into the grid as per the despatch schedules, which also involves must-run power plants such as renewable energy sources.