Study Report on FGD Implementation: IIT Delhi

Emissions from coal-based thermal power plants (TPPs) are known to have adverse impacts on the environment and human health. Combustion of coal in these TPPs releases sulfur dioxide (SO2), nitrogen oxides (NOx), carbon monoxide (CO), and various primary particulate matter (PM) into the air through stacks that can disperse this pollution over large areas.

On December 7, 2015, the prevailing norms regarding air pollution from TPPs were revised and new norms regarding limits of PM2.5, SOx, NOx, and mercury emissions from TPPs were introduced. After notification of new emission norms, it has become necessary for several TPPs across the country to install flue gas desulfurisation (FGD) units to curtail the emission of SO2 from the stacks to comply with the above stipulated SO2 emission limits. This report presents a study to assess the compliance of TPPs across India to the new SO2 emission norms (2015) and lay out a phased plan for FGD implementation in TPPs across the country.

A detailed analysis of stack emissions and ambient air quality data from 240 stacks from 67 coal-based TPPs across the country is performed in this study. A detailed analysis of SO2 and sulfate (SO4) aerosol data over the Indian region has been performed using satellite observations, emission inventory, and reanalysis data sets to identify areas within the country which has the highest column burden and surface concentration of SO2 and sulfate (SO4) aerosols. Additional model sensitivity simulations are performed to investigate and understand the sensitivity of dispersion of SO2 from a selected TPP as a function of different choices of stack height. The report further investigated the impact of the implementation of FGD in coal-based TPPs across the country on the near-surface concentrations of two major air pollutants, namely SO2 and sulfate aerosols, in the surrounding region of these TPPs by conducting chemical transport model simulations using the weather research forecast model coupled with an atmospheric chemistry module.

The study finds that while implementation of FGD in TPPs can result in significant decreases (up to 55%) in SO2 concentrations that are mostly confined in the immediate surrounding areas of the TPP and up to a maximum distance of 60-80 km from the location of the TPP and in the direction of maximum dispersal of the air pollutants but, significant decreases (up to 30%) in the surface concentrations of sulfate (SO4) aerosols can be expected at locations which could be as far as 200 km from the location of the TPP. A series of systematically designed WRF-Chem model simulations are performed to carry out source apportionment of air pollutants for Delhi National Capital Region (NCR). The results suggest that while the maximum contribution to SO2 surface mass concentration over Delhi NCR for the December month came from the energy sector emissions (~63%), the maximum contribution to sulfate (SO4) aerosol surface mass concentration over Delhi NCR for the same month came from the transportation sector emissions (~33%) followed by the energy sector emissions (26%).

Finally, considering the challenges involved in implementing FGDs in all TPPs across the country simultaneously, it is recommended to adopt a graded action plan for phased implementation of FGDs by giving preference to areas that have the highest surface concentration of SO2 as per the analysis of satellite observations and MERRA2 reanalysis data. The implementation of FGDs in all coal-based TPPs across the country is recommended in five phases. Phase 1 of FGD implementation should be of 3-year period from July 2022 to July 2025 and it should include FGD implementation in around 40 TPPs across the country. After Phase-1, a study must be conducted to ascertain the performance of these FGDs at least over a period of the next one year and confirm the tangible benefits of installation of FGDs in TPPs by considering its impact on extra CO2 emission, accelerated warming of the regional climate, extra water consumption, limestone mining, transportation of limestone from the mines to the TPPs, and disposal of byproducts like gypsum etc. Phase-2 of FGD implementation should happen in around 49 TPPs should start from July 2026 and completed by July 2029. A four-year time period between start of the Phase-1 and Phase-2 of FGD implementation will also allow seeing the emergence of new FGD technologies which could possibly consume less water, avoid any extra emission of CO2 into the atmosphere etc. Thereafter Phase 3 can be implemented in around 27 TPPs from July 2029 to July 2031. Phase 4 should happen in around 21 TPPs from July 2031 to July 2033. While Phase-5 should happen for the remaining 7 TPPs from July 2033 to July 2034. While the reduction in SO2 emissions from TPPs by FGD implementation is highly desirable, it is also equally important to ensure that the benefit of SO2 emission reduction is not coming at a cost of increased emission of greenhouse gases, extra consumption of valuable water, accelerated global warming, and various other problems associated with it.

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