Considering that thermal power plants (TPPs) are responsible for the majority of emissions, the reduction of pollutants such as SOx, NOx and particulate matter (PM) is one of the top goals of power plant operators. Due to the characteristics of Indian coal, which includes very high resistive dust and low sulphur content, the issues are compounded. The overall compliance with the emission standards notified by the Ministry of Environment, Forest and Climate Change (MoEFCC) in December 2015 has been modest to date. In April 2021, the MoEFCC released a new order defining location- and category-wise compliance deadlines. The majority of TPPs now have until December 2024 to comply with the emission standards.
Power Line takes a look at some of the recent developments and challenges in the installation of emission control systems…
The MoEFCC, in April 2021, extended the deadline for complying with the emission norms for coal-based power plants by one to three years, based on the location of the plant. As per the Environment (Protection) Amendment Rules, 2021, power stations have been divided into three categories. Category A TPPs, comprising plants within a 10 km radius of the NCR or cities that have a million-plus population, are required to meet the emission norms by December 2022. Category B TPPs, comprising plants within a 10 km radius of critically polluted areas or non-attainment cities, have to meet the norms by 2023. Category C is made up of the rest of the plants, which have been given an extension till 2024. Apart from this, TPPs that are declared to retire before December 31, 2025 are not required to meet the specified norms. Such plants need to submit an undertaking to the Central Pollution Control Board (CPCB) and the Central Electricity Authority (CEA) for exemption on the ground of retirement.
A task force constituted by the CPCB has categorised 600 coal-based units. Accordingly, 66 coal-based units fall under Category A with a compliance deadline of December 2022, 72 fall under Category B with a compliance deadline of December 2023 and 462 fall under Category C with a compliance deadline of December 2024. The majority of the capacity (around 77 per cent) falls under Category C and the remaining coal-based capacity falls under Categories A and B.
FGD installations across India
According to the CEA’s data, flue gas desulphurisation (FGD) systems have been commissioned and are operational for 8,290 MW of capacity. Under Categories A and C, FGD systems have been installed for 2,910 MW and 5,380 MW of coal-based units, while none has been commissioned under Category B. Bids have been awarded for 190 units aggregating 85,740 MW of capacity. Apart from this, a notice inviting tender has been issued for 32,135 MW and feasibility studies have been completed for 21,345 MW.
Issues and challenges
The FGD market in India is evolving and there is limited availability of vendors. Overbooking of suppliers has resulted in an increase in manufacturing timelines for FGD equipment. There is a dependency on imports from neighbouring countries, and certain import restrictions have been imposed. With regard to equipment availability, the domestic manufacturing capacity is not adequate for equipment such as agitators, gypsum dewatering systems, borosilicate and clad plates. The recent notifications, which restrict procurement from neighbouring countries, has had an adverse impact on procurement costs and timelines since these items have high lead times and a limited supplier base. In addition, due to changes in the procurement policy and stringent prequalification norms as per the government’s guidelines, price offers from prospective domestic suppliers have increased. The ordering cycle has also been adversely affected, impacting both the time and the cost of the project.
Further, FGD orders envisage retrofitting of FGD components in brownfield projects. Retrofitting of FGD components face issues relating to conceptualisation and design. Standardisation could help overcome this issue, but it has not been done as different sites have different requirements owing to space, geography, orientation, etc. Retrofitting of FGD components is more like renovation and modernisation, which encounter frequent reengineering issues. In addition, the availability of drawings for old plants during retrofitting remains a challenge.
Moreover, due to the huge gap in the demand and supply of FGD equipment, the prices of raw material and FGD components are escalating significantly. Base materials such as steel, cement, nickel, aluminium and copper have seen a surge in prices, resulting in an increase in the cost of tanks, ducts, pipe racks and supporting structures. The impact of Covid-19 on planning, placing of orders, supply chain of equipment and installation of FGD systems has also been quite severe. Also, many subcontractors, and indigenous and foreign vendors have gone into distress due to pandemic-led work disruptions. All these factors are likely to ultimately lead to higher costs of electricity.
Impact of FGD retrofits
As per an IIT Delhi study, there is a 65-85 per cent decrease in SO2 levels in the ambient air up to at a distance of 10-40 km (depending on the sulphur removal, as per the norms applicable to TPPs), whereas the reduction of SO4 in ambient air is about 12 per cent at a distance of 200 km. However, CO2 emissions per unit of power generated by coal-based TPPs are likely to increase with FGD implementation. The primary reason for this is that for every molecule of SO2 absorbed, a molecule of CO2 will be released into the atmosphere in all desulphurisation processes. Additionally, about 0.5 per cent SO2 in Indian coal will produce an additional 0.5 per cent of CO2 burden.
FGD installation leads to an increase in auxiliary power consumption of about 1 per cent. Therefore, coal consumption in TPPs is likely to increase by at least 1 per cent due to increases in auxiliary power consumption, depending on the FGD technology implemented in the TPP, leading to more greenhouse gas or CO2 emissions. FGD installations also lead to an increase in water consumption of about 0.5m3 per MWh. FGD installations require limestone for neutralisation of SO2. Transportation of limestone by rail consumes electricity, which, in turn, burns coal and generates CO2. In addition to this, during the mining of limestone, dust is generated (PM10, PM2.5), which impacts the environment. Further, FGD installations require a capex of about Rs 2 trillion, which will result in an increase in electricity tariff across the country. The cost of wet limestone-based FGD systems is around 14 million per MW, which will lead to an increase in electricity tariff of around Re 0.71 per kWh.
The way ahead
Considering the challenges involved in implementing FGD systems in TPPs, the CEA has suggested that ambient air quality should be made the guiding factor for formulating SO2 emission control norms in TPPs. This may avoid the installation of additional emission control equipment without compromising air quality. The CPCB has categorised SO2 concentration into five levels, ranging from 0 µg/m3 to 40 µg/m3. Level-I has an SO2 concentration of over 40 µg/m3, Level-II has an SO2 concentration of 31-40 µg/m3, Level-III has an SO2 concentration of 21-30 µg/m3, Level-IV has an SO2 concentration of 11-20 µg/m3, and Level-V has an SO2 concentration of 0-10 µg/m3.
The CEA has recommended a phased implementation of FGDs, giving preference to areas that have the highest surface concentration of SO2. To achieve tangible results, the SO2 emission control equipment in Level-I TPPs must be installed on a priority basis. The regions identified under Level-II can be covered subsequently in the next phases, based on the performance of the FGD systems in Level-I. It suggests that the second phase of FGD system installation may be initiated three years after the commissioning of the first phase, which gives time for course correction based on the performance in the first phase. At present, no action is required for plants under Levels III, IV and V as the SO2 emissions in the ambient air of these areas are much lower.
In addition, it recommends that an annual FGD system implementation target should be decided considering the available vendors’ capacity, which is estimated to be 15-17 GW (32-36 units) per annum at present. Therefore, the CEA has proposed to extend the timeline up to 2035 for smooth implementation of FGD systems.
To conclude, while reducing SO2 emissions from TPPs through FGD implementation is highly desirable, it is equally important to ensure that the benefits of the reduction do not come at the cost of increased emissions of greenhouse gases, higher consumption of valuable water, accelerated global warming, and various other problems associated with it. n
With inputs from a presentation by B.C. Mallick, Chief Engineer, Central Electricity Authority, at a recent Power Line conference