Some stories are never ending, and so is the story of how to check pollutant emissions. Since April, debates and discussions have been taking place between the Ministries of Environment and Power over the relevance of FGD (flue gas desulfurisation), meant to control sulphur dioxide (SO2) emissions from coal-fired thermal power plants.

The Ministries have directed the Central Pollution Control Board (CPCB) to have a close look at FGD and to assess the three different studies done by IIT Delhi, CSIR-NEERI (who were asked by NITI Aayog) and National Institute of Advanced Studies (NIAS), Bengaluru, respectively, on it.

All three reports seem to have reached the same conclusion. They have recommended against FGD installation in Indian thermal power plants, citing low sulphur in Indian coal, compliance with National Ambient Air Quality Standards for SO2, and minimal impact on particulate matter reduction.

FGD is a process used to remove SO2 from the flue gas produced when burning fossil fuels such as coal or gas. But with constant upgradation of technology to increase efficiency and reduce pollution, industry has been seeking a reconsideration of the norm.

Where did it start?

According to Section 7 of Electricity Act 2003, any generating company can establish, operate, and maintain a generating station without obtaining a licence under the Act, if it follows the technical standards relating to connectivity with the grid referred to in clause (b) of Section 73 of the Act. All thermal power plants must follow the emission norms as notified by the Ministry of Environment, Forest and Climate Change (MoEF&CC) and directions given by CPCB from time to time.

MoEF&CC notifications dated December 7, 2015, March 31, 2021, and September 5, 2022, have stipulated stack emission norms (including for SO2), timelines for compliance and environmental compensation (in case of non-compliance) in respect of these plants based on categorisation.

MoEF&CC has prescribed timelines for FGD installation based on the plant’s capacity and installation date: For plants installed before December 31, 2016, the deadline is December 2025; while for plants installed after January 1, 2017, it is December 2026.

Though committed to the carbon reduction protocols, the industry (mainly thermal power plants) have argued that implementation of FGD should be backed with scientific efficacy, particularly in the Indian context where the sulphur (0.5 per cent) content in domestic coal is low.

Besides, there cannot be a generic norm for all plants to follow since the ambient SO2 concentrations attributed to each plant could vary depending on the sulphur content of the coal used as well as the regional climate. The three independent studies prove with different case studies and methods that FGD hardly has any impact on particulate matter pollution, which is a major problem attributed to thermal power plants using high ash Indian coal.

This leads us to the question: Why at all was the decision to install FGD taken, and was there no assessment done by CPCB before this call was made?

Low sulphur content

According to R Srikanth, Professor and Dean of the School of Natural Sciences & Engineering, National Institute of Advanced Studies, Bengaluru, and co-author of the NIAS study, while FGD can reduce SO2 emissions from thermal plant stacks, the ambient SO2 concentrations in the country are generally much below the National Ambient Air Quality (NAAQ) Standards even without FGD. The low levels of SO2 in the ambient air are due to the extremely low sulphur content of Indian coals (barring Assam and Meghalaya) and the efficient dispersion of SO2 emissions from thermal plant stacks in India, he said.

In 1985, CPCB published the results of a study to find the minimum height of the stacks (chimneys) to limit ground-level concentrations of SO2. Based on this study, the minimum height of the stack was fixed at 220 m for 200-490 MW plant and 275 m for 500 MW (and above). This mandate is being followed for all thermal plants installed after 1984, which has resulted in limiting ambient SO2 around plants to much below NAAQ standards.

While SO2 converts into sulphate particles in the atmosphere, CPCB did not publish any study to assess the proportion of sulphate particles in particulate matter pollution attributable to plants outside Delhi before promulgating the nationwide 2015 Thermal Power Plant standards, which have enormous implications on electricity tariffs and global warming, says Srikanth.

Critics say that the CPCB has only followed up on installing FGD to control SO2 emissions from the plant stacks rather than enforcing compliance with the stack emission standards for particulate matter pollution, even though stack emissions from these plants can be reduced by 99.97 per cent by retrofitting plants with high-efficiency electrostatic precipitators (ESPs).

On the other hand, installing FGD increases CO2 emissions from plants by increasing their auxiliary power and specific coal consumption, he said, adding “Installing FGDs in all thermal plants in India will impact global warming by removing the coolant sulphate aerosols that mask global warming, per the 6th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR 6).”

Wet FGD needed for inland plants also enhances the water consumption of the plants when the power sector is mandated to reduce freshwater consumption, he argues.

It is, therefore, questionable whether we should mandate the installation of costly, water-guzzling FGD technology in all plants when India is committed to reducing the power sector’s CO2 emission intensity, says Srikanth. “The focus must be on enforcing compliance with the NAAQ standards nationwide rather than stack emissions of SO2. This requires CPCB to shift its attention away from FGD to the retrofit of high-efficiency ESPs in all plants within the next three years,” he said.

The NIAS study recommends that particulate matter from thermal power plant stacks can be addressed quickly and cost effectively by retrofitting indigenous ESPs in all thermal power plants irrespective of their size or location

High installation cost

For installing FGD, a plant needs to be shut down for at least 45 days. This means revenue loss for the plant, which will be passed through in the tariff. Instead, high-efficiency ESPs can be retrofitted in all plants and hooked up to operating plants with a two-day shutdown.

The installation of ESP will cost ₹25 lakh per MW against ₹120 lakh per MW for wet FGD based on imported technology, the study shows. It also recommends that the thermal power plants retiring by 2030 should be exempted from SO2 stack emission norms since these will be normally obsolete stations with a proportionately lesser contribution to total electricity generation in the country. This will avoid saddling electricity consumers with large tariff hikes to recovery the FGD cost within a brief period.

While the authorities are debating the issue, an ideal solution is to have a clear strategy even for implementing FGD and simultaneously promote the use of cleaner coal and thus have a balanced energy mix.

Published on May 5, 2025