Old thermal plants may get flue gas desulphurisation exemption

CHENNAI: The Central Electricity Authority (CEA) has recommended that old coal-fired power plants be exempted from installing flue gas desulphurisation (FGD) systems if they are operated flexibly to support the integration of renewable energy.

The Committee Report on Wear & Tear, O&M, and Plant Lifespan Implications of Two-Shift Operations in Thermal Power Plant’s recommendation comes against the backdrop of the Union ministry of environment, forest and climate change (MoEF&CC) relaxing the timelines for complying with sulphur dioxide (SO2) emission standards through a notification issued on July 11, 2025. 

The revised rules gave thermal plants more time to install FGD systems and exempted units officially declared for retirement before December 31, 2030. Under this, Category A plants located within 10 km of cities with a population of more than one million have to comply with SO2 norms by December 31, 2027.

Category B plants in critically polluted areas will be assessed individually and, if not exempted, have to install FGD systems and comply by December 31, 2028. Category C plants are exempt from mandatory FGD installation, subject to meeting stack-height requirements by December 31, 2029.

The CEA committee has now proposed exempting identified old Category A and B plants from FGD requirements if they are used for integrating renewable energy. These plants would shut down during the peak solar generation period, broadly between 9 am and 4 pm or 10 am and 5 pm, and restart in the evening to meet peak demand.

The two-shift model would mean that instead of running at low load throughout the day when solar power is available, the old coal units would be taken off the grid during the solar peak and brought back during the non-solar period. The report said the plants would have a plant load factor of around 60% and would generally use hot starts when restarting each day.

The committee noted that two-shift operation comes with higher costs and accelerated equipment wear because of daily shutdowns and startups. However, it said the older plants, particularly those with near-zero fixed costs or fully depreciated capital costs, could economically be retrofitted for such operation. Since they would remain in operation for only around 16 hours a day, their overall emissions would also be lower than those of plants running for longer periods at low loads.

Tamil Nadu’s 5x210 MW Tuticorin Thermal Power Station (TPS) is one of the key examples cited in the report. CEA and BHEL jointly studied the plant’s two-shift operation and found that its units generally stop generation between 7.20 am and 11.45 am and restart between 3.31 pm and 7.14 pm, depending on system requirements.

The study also quantified the cost of making coal units flexible. Shutdown and startup costs were assessed at 29.42 paise per kWh, while increased O&M costs were 16.68 paise per kWh. Retrofitting was estimated to cost Rs 120 crore to Rs 250 crore per unit. Depending on the investment, the total tariff impact was estimated at 62.24 paise to 79.95 paise per kWh for a 210 MW unit, based on a 12-year payback period.

The committee has identified 151 coal-based generating units totalling 34.5GW and aged 35 years or more for possible two-shift operation. It estimates that the model could provide about 24GW of flexible power or storage to the grid and help accommodate the projected growth in solar generation.

The FGD exemption recommendation is based on the committee’s assessment that these plants would have a significantly reduced operating window and lower daily average emissions while serving as firm backup when renewable generation falls.