Reducing mercury emissions from coal-fired power plants in India: Possibilities and challenges

Abstract

Coal combustion is the largest source of power in India at the moment. This combustion also emits trace amounts of hazardous substances such as mercury. Mercury is a global pollutant with the potential for long-range transport and ability to persist in the environment, bioaccumulate and cause toxicity. Controlling emissions of mercury from coal-fired power plants (CFPPs) is recognized by the Minamata Convention on Mercury as an important step in curbing the harmful effects of mercury to the environment and humans. India has been identified as one of the top emitters of mercury to the atmosphere, and coal combustion contributes to more than half of these emissions. Here, we discuss the current state of regulations on mercury emissions from CFPPs in India, the current information on mercury from CFPP stacks, and the possible way forward. Present data suggest that mercury specific emission control technologies are not required to comply with the regulatory requirements. As such, any reduction in mercury emissions will rely on co-benefits obtained from technologies to control emissions of other pollutants such as flue gas desulphurization, or methods to increase the efficiencies of CFPP such as coal washing. Additional reductions may be made from a business-as-usual scenario if the energy mix of India changes to renewable non-fossil fuel-based energy at an accelerated pace. Quantitative studies assessing the role of such climate change policies on mercury emissions reduction are recommended.

Introduction

Approximately 300 million people in India were without access to power in 2015 (Gowen 2015). Continuous availability of energy sources is critical to resolve the disparity in access to power and fulfil the objectives of economic development and increased standard of living including moving people above the poverty line. The electrical power sector in India is dominated by fossil fuels, especially coal, which produces more than half of the country’s electricity (Tiewsoh et al. 2019; Seetharaman 2020; Government of India and Ministry of Power 2022). However, the electricity from fossil fuels comes at a high social and environmental cost (Munawer 2018). Harmful emissions such as greenhouse gases, oxides of nitrogen and sulphur, and mercury and other heavy metals are released (Munawer 2018). Local, regional and global environmental pollution from coal-fired power plants (CFPPs) is a matter of concern.

Coal combustion is the largest source of mercury emission to air in India, contributing to more than 50% of total atmospheric emissions (Burger Chakraborty et al. 2013; Vishwanathan et al. 2018). Mercury emitted from CFPPs may travel long distances prior to its deposition and cause global contamination (Schroeder and Munthe 1998; Lindberg et al. 2007; Sharma et al. 2019; Vijayaraghavan et al. 2021); thus, mercury becomes one of the major global air pollutants. Since mercury is a global pollutant due to its persistence, bioaccumulation, toxicity and long-range transport, a global regulatory system to reduce the harmful impacts of mercury, the Minamata Convention on mercury was adopted in 2013 (UNEP 2017). The convention aims to regulate the release of mercury and its compounds to the environment, and manage and mitigate the associated environmental and human health problems.

India ratified the Minamata Convention in 2018. Consequently, the country has a responsibility to control the release of mercury into the environment. Here, we present a commentary on the available information on mercury emissions from CFPPs in India, and how different actions by the government and industry align with the emission reductions goals and methods stipulated in the Minamata Convention. Namely, we address the status of different governmental emission norms, and emission reduction technologies implemented or being implemented and their potential impacts on mercury emission reductions, and a future outlook on mercury emissions control in India.

Minamata convention and Indian coal-fired power plants

The Minamata Convention aims to protect human health and the environment from anthropogenic emissions and releases of mercury and its compounds (UNEP 2017). According to the 2018 Global Mercury Assessment, human-made sources have directly or indirectly affected the emissions of about 90% of total mercury into the air (UN Environment 2019). Burning of fossil fuel, primarily stationary coal combustion, is the second-largest source of mercury pollution to air and accounts for an estimated 21% of global atmospheric emissions (UN Environment 2019). Article 8 of the Minamata Convention considers CFPPs as one of the (important) point sources of mercury in the environment and directs parties to adopt appropriate strategies to reduce mercury emissions and its compounds. As such, reducing mercury emissions from coal combustion will go a long way in reducing the overall global mercury pollution.

The coal-based electricity generation capacity of India has increased from 800 MW (Agrawal et al. 2008) in 1973 to 204 080 MW in 2022 (Government of India and Ministry of Power 2022). According to the government, constructions are ongoing in CFPPs to generate 62 200 MW of additional power (Government of India and Ministry of Environment, Forest, and Climate Change 2020). The government policies for rural electrification rely on an increase in total power generation of the country, and CFPPs appear be an integral part of the plan. Overall coal-fired power generation capacity is expected to increase by 23%, by 2030 compared to 2022 (Shah 2021a). Subsequently, the demand for coal in for use in CFPPs is also increasing year after year. For instance, of the total 676 million tonnes of coal mined, India dispatched 75% of its mined coal to power utilities in 2017–2018, and 76.5% of the 730.8 million tonnes mined coal to power utilities in 2019–2020 (Ministry of Coal 2019, 2021).

The mercury content of Indian coal produced by different mines varies according to geographical features. A study in 2014 (UNEP 2014) suggested that mercury concentration in coals ranged from 0.003 to 0.34 g/tonne (g/t) with an average of 0.14 g/t, while another study reviewed that Indian coals have mercury contents ranging from 0.11 g/t to 0.80 g/t (Sloss 2012b; UNEP 2014). Another study (Mishra et al. 1997) reported the concentration of mercury in coal to be from 0.01 to 1.1 ppm, as against up to 2.0 ppm in Russian Coals, 0.2 to 2.0 ppm in Belgium coals, 0.03 to 1.3 ppm in Canadian coals, and 0.01 to 1.8 ppm in American coals (Tewalt et al. 2001; Agrawal et al. 2008). Most of these studies conclude that the concentration of mercury in Indian coal is comparatively lower than others. It also seems that this concentration is very variable. The natural variabilities and characteristics of coal may be the reasons for differences in mercury content of Indian coal. They also affect the estimation of total mercury emissions and mobilization. A 1% increase in the mercury concentration of coal could mobilize an extra 1.75 tonnes in 2010 (Burger Chakraborty et al. 2013). So, this uncertainty over mercury content in coal could create difficulties in developing strategies to reduce mercury emissions.

Mercury reduction measures

The Minamata Convention does not specify quantitative emissions limits or require specific technologies. Instead, it stipulates that parties must adopt feasible best available techniques and environmental practices in new CFPPs to control mercury pollution (UNEP 2017). Additionally, the Convention provides liberty to parties to determine the means to reduce mercury emission from the existing CFPPs within ten years without affecting the country’s developmental aspirations. The Article 8(5) of the convention suggests five measures to adopt for the effective reduction of mercury from existing CFPPs, considering the economic and technical feasibility and affordability of the measures (UNEP 2017). These are: fixing quantified goals, defining emission limit values, adopting multi-pollutant control strategies, implementing best available techniques and environmental practices, and using other alternative reduction measures. The following sections will report the current situation in India with respect to these five measures.

Fixing quantified goals

Each party to the Minamata Convention is expected to prepare a Mercury Initial Assessment (MIA). This MIA would be expected to provide the inventories in, and flows of mercury from, different components of the country’s anthroposphere. These may include mercury in stocks, either raw or as part of mercury-laden products, emissions of mercury from various anthropogenic activities to air, water, and land, mercury in landfills, in hospitals, educational institutes, and the corresponding flows. With these quantified emissions and inventories as baseline, a country can choose to provide quantified reduction targets, be it for emissions, fluxes, or inventories. At the moment, India has not submitted its MIA with official numbers (UNEP 2022). Therefore, quantification of goals without this baseline may not be precisely possible. As such, results from the first MIA containing legitimate official numbers on mercury emissions, inventories, and fluxes are urgently needed.

Introduction of emission limits

Several countries rely on emission limit strategies as significant measures for pollution control because of its convenience in monitoring (Rallo et al. 2011; Ministry of Ecology and Environmental of the People’s Republic of China 2012). However, setting off a diluted emission limit might affect pollution control measures negatively, while adoption of a strict emission standard might create a heavy financial burden or technological deterioration in coal plants. In 2015, the Indian government introduced emission standards (Table 1) for limiting sulphur oxides, nitrogen oxides, particulate matter and mercury emissions in CFPPs (PIB 2020).

Table 1.

New environmental emission norms (Ministry of Environment Forest and Climate Change 2015)

Date of installation	PM	SO2	NOx	Hg
Before 31-12 2003	100 mg/Nm3	600 mg/Nm3 for < 500 MW 200 mg/Nm3 for >  = 500 MW	600 mg/Nm3	0.03 mg/Nm3 for > = 500 MW
From 01-01-2004 to 31-12-2016	50 mg/Nm3	600 mg/Nm3 for < 500 MW 200 mg/Nm3 for >  = 500 MW	300 mg/Nm3	0.03 mg/Nm3
On or after 01-01-2017	30 mg/Nm3	100 mg/Nm3	100 mg/Nm3	0.03 mg/Nm3

The promulgated mercury standards are comparable to the norms set in China (Sloss 2012a; Ministry of Environmental Protection and State Administration for Quality Supervision and Inspection and Quarantine 2011). The new pollution standards are expected to help reduce mercury emissions from new CFPPs by 75% (Nagar 2015) and particulates matter by 25%, SO2 by 90% and NOx emissions by 70% (Sloss 2015). Indian mercury emission norms are less strict than US (0.4 μg/m³ to 5.08 μg/m³, depending on the coal) and Canada (2.3 μg/m³ to11.6 μg/m³) (USEPA 2020; Wu et al. 2018).

Moreover, and importantly, concentrations of mercury in flue gases from four bituminous coal-fired and one lignite-fired power plants in India have been observed to be in the range of 9–29 μg/Nm³ which is lower the proposed threshold limit (30 μg/Nm³) (Agarwalla et al. 2021). All these power plants contained only fabric filter/electrostatic precipitators (ESPs) as pollution control devices, and none contained any additional pollution control method either specific to mercury or which helps in co-removal of mercury. The observations of Agarwalla et al. (2021) suggest that it is likely that mercury reductions may not be needed to be specifically targeted by any CFPP; they would already be complying with the emission limits. Thus, the proposed emission norms may not be effective in reducing mercury emissions. Mercury emissions’ reductions from CFPPs will be at the mercy of co-removal from other pollution control methods.

Initially, the emission norms were expected to be implemented by 2017 (Ministry of Environment Forest and Climate Change 2015), but later the implementation was delayed to 2022 (CSE 2021a; Ministry of Environment Forest and Climate Change 2019). Recently, the Ministry of Environment Forest and Climate Change again extended the deadline of compliance for most of the CFPPs to 2024 (Ministry of Environment Forest and Climate Change 2021). The recent notification has distinguished coal-power plants into three categories, Category A, B, and C. CFPPs located in a 10-km radius of the National Capital Region, or cities with a million-plus population as per the 2011 census, come under Category A. Category A CFPPs have to meet the emission norms within 2022. CFPPs within a 10-km radius of Critically Polluted Areas or Non-Attainment Cities (cities where the Indian National Ambient Air Quality Standards are violated) come under category B, and the rest of the CFPPs are in Category C. The deadlines for Category B and C are 2023 and 2024, respectively. A Non-Governmental Organization opined that only 27% of the power plants come under Category A. So, the new extension meant 73% of the CFPPs continue to pollute for another 2–3 years (CSE 2021a).

The most recent government notification also introduced a penalty mechanism, termed environmental compensation, for non-compliance. This suggests that CFPPs can continue to operate by paying penalties after the extended deadline. This notification also contains provisions about the retiring power plants. It stipulates that the old CFPPs in category A must retire by 2022, and all other old CFPPs can continue until 2025. Retiring CFPPs, except those in Category A, were exempted from installing pollution control systems by submitting an undertaking to retire.

However, this does not mean that the plants will be forcibly shut down after the deadline. They would be allowed to function without meeting the norms as long as they pay the penalty. Some have suggested that the penalty cost is much lower than cost of installing pollution control equipment (CSE 2021a). Thus, instead of adopting pollution control technologies, CFPPs can potentially adopt a strategy paying cheaper penalties (Nandi 2021; CSE 2021b). Speaking tersely, the notification may indirectly give the CFPPs a license to pollute rather than ensure compliance with pollution standards.

Multi pollutant control strategies

The characteristics of Indian coals affect the removal of the mercury from coal. When coal combusts in boilers at high temperature, the majority of mercury in coal is released as elemental mercury, and depending on the chemical composition of the coal (presence of sulphur and other halogen elements) and thermochemical process, a fraction of elemental mercury is converted into oxidized mercury and particle-bound mercury. The remaining elemental mercury is difficult to remove by air pollution control devices (Agarwalla et al. 2021). Oxidized mercury and particle-bound mercury can be removed from flue gas (Agarwalla et al. 2021). The Indian coals are characterized as with high ash content, high moisture content, low sulphur content, low halogen content, and low calorific values (Kumari 2010). The high ash content and low calorific value affect the CFPP’s operational efficiency and increase emissions (Guttikunda and Jawahar 2014). The high silica and alumina content in Indian coal ash increase ash resistivity and reduce the collection efficiency at the electrostatic precipitators, which are the most common Air Pollution Control Device (APCD) in Indian CFPPs (UNEP 2014; Guttikunda and Jawahar 2014).

A majority of CFPPs in India are only equipped with electrostatic precipitators, used to capture particulate matter (Sloss 2012b; UNEP 2014). Others employ fabric filters (FFs) as the particulate matter-capturing devices. Mercury removals efficiency is generally considered to be approximately 27% to 58% in such APCDs (Pavlish et al. 2003). Therefore, the existing mercury emission reduction from Indian CFPPs is due to the co-benefit effects obtained from basic particulates matter control systems. Giang et al. (2015) estimated that the existing emission control practices in Indian CFPPs only provide a mercury efficiency of 42% to 58% and suggested the introduction of other stricter policies for achieving substantial benefits on mercury emissions reduction.

The APCDs for control of sulphur emissions, such as wet flue gas desulphurisation (wFGD), effectively capture mercury (Hall et al. 2007; UNEP 2011; Laudal et al. 2012). FGD systems have been shown to remove 80–90% of oxidized mercury, despite ineffective in removal of elemental mercury (Pavlish et al. 2003). Configurations combining FGD with ESPs, or FFs, have been shown to achieve mercury capture efficiencies of up to 80%, or 95%, respectively (US EPA and Office of Research and Development 2005) (Table 2). Overall, FGD captures a large percentage of oxidized mercury present in coal-fired combustion flue gas because the oxidized mercury is soluble in the calcium-containing liquid solution in the FGD (ICAC 2011). The concentration of sulphur in flue gas and solid oxides in the scrubber influences mercury capture from the CFPPs (Díaz-Somoano et al. 2005; Ochoa González et al. 2012). Higher sulphur and halogen contents in coal affect mercury speciation between the oxidized and elemental forms; higher sulphur and halogen oxides lead to higher oxidized mercury percentages (Keiser et al. 2014). In general, coal with more than 500 parts per million weight (ppmw) of chlorine exhibits a higher mercury oxidation rate than coal with more than 100 ppmw of chlorine (Miller et al. 2006; Adams and Senior 2006).

Table 2.

Possible Mercury control technologies for the conventional coal-fired technologies in the United States and the mercury removal efficiency

Control technologies	Mercury removal efficiency (%)
	Bituminous	Sub-bituminous	Lignite	All coals
Cold side ESP*	30–40	0–20	0–10	0–40
Cold side ESP + FGD*	60–80	15–35	0–40	0–80
Fabric Filter*	40–90	20–75	0–10	0–90
Fabric Filter + FGD*	75–95	30–75	10–40	10–95
FGD**	42	30	–	–
SCR + FGD**	90	51	–	–
ESP + SCR + FGD**	90	66	44	–
Coal cleaning*	20–40	–	–	0–40

^*(Pavlish, Hamre, and Zhuang 2010) **(ICAC 2011)

At present, the use of flue gas desulphurisation is in a nascent stage in India. After the notification of new emission norms (Ministry of Environment Forest and Climate Change 2015), the installation of FGD has become essential in CFPPs for compliance with stipulated SO₂ emission limits. The Ministry of Forest and Climate Change is accelerating the installation of FGD systems in CFPPs (Siwal 2017; Ministry of Environment Forest and Climate Change 2018; Behi 2019), which will expected to concomitantly removal mercury as well. The country’s largest power producer, NTPC, is installing FGDs in all of its power plants across the country (PTI 2019). Studies by Giang et al. and Burger Chakraborty et al. have estimated that the introduction of FGD in Indian power plants would increase the mercury capture efficiency of CFPPs from 58% to 70.5% and 40% to 70%, respectively (Burger Chakraborty et al. 2013; Giang et al. 2015). This indicates that introduction of FGDs could be the next logical step for reducing emissions of mercury to the atmosphere in India. However, Burger Chakraborty et al. also noted the possibility of a simultaneous increase in the mercury pollution of soil and water, because installation of FGDs would mean that the flow of captured mercury into land, water, and anthropogenic sinks will increase (Burger Chakraborty et al. 2013).

The capital cost for the instalment of FGDs also affects the pace of the implementation. An environmental NGO estimated the total capital cost of installing pollution control technology in CFPPs to be approximately INR 2 577 000 000 000 (USD 35 billion) (Srinivasan et al. 2018; Oundhakar 2019). That is, an approximate expenditure of INR 5 000 000–6 000 000 (USD 70 000–80 000) per MW (Srinivasan et al. 2018; Oundhakar 2019).

Selective catalyst reduction (SCR) and selective non-catalytic reduction (SNCR) are used in thermal power plants to reduce the emission of nitrogen oxides (Laudal et al. 2012). These systems could also convert elemental mercury to oxidized mercury. It is observed that the SCR control devices oxidize 30–98% of elemental mercury in CFPPs firing bituminous coals, and a much lower percent of elemental mercury in CFPPs firing sub-bituminous coal (Senior 2006).

Several factors influence mercury oxidation in the SCR catalysts, such as flue gas components, particularly the amount of mercury and halogen, the composition of the SCR catalysts, and the temperature of the power plant (Fernández-Miranda et al. 2016). Consequently, several approaches are in practice to maximize the oxidation capacity of SCR. Higher elemental mercury oxidation could be obtained by blending low chlorine coal with high chlorine coal, injecting different halogen-containing additives into the flue gas, or adding bromide salts to the coal (Dranga et al. 2012). CFPPs also use a combination of SCR and wet FGD to enhance mercury capture. High levels of oxidized mercury and total mercury capture were achieved commercially when firing bituminous coal on units equipped with SCR and FGD when halogen levels in the coal were relatively high (ICAC 2011). The combination of SCR with wet FGDs was reported to reduce the mercury emissions by 51% to 90% (ICAC 2011; Madsen et al. 2011). This technology has not yet been used with Indian coals because of the concern over the high ash content of Indian coal (Wiatros-Motyka 2019). Nevertheless, studies are underway to customize these technologies for the Indian Market (Wiatros-Motyka 2019). Recently, Bharat Heavy Electricals Limited conducted a pilot test of SCR facilities for NOx control which used Indian coals with an ash content of above 40% (Wiatros-Motyka 2019). Overall, mercury removal efficiencies also depend on whether SCR is present upstream or downstream of the FGD. When an SCR system is present upstream of an FGD unit, it oxidizes mercury and, thus, enhances the capture mercury in the FGD system (Díaz Somoano 2019).

Other control technologies such as activated carbon injection (ACI) explicitly target for the capture of mercury, particularly elemental mercury, from CFPPs (Sargent and Lundy 2011). In general, dedicated mercury removal technologies are considered more expensive because they have high operational and maintenance cost (Pacyna et al. 2010). In ACI, activated carbon (often impregnated with a halogen) is injected in the particulate matter control device and aids in additional capture of mercury (Pacyna et al. 2010; Giang et al. 2015). It can provide up to approximately capture 95% of mercury in coals with higher chlorine contents (Moretti and Jones 2012). Chemical modification of powdered carbon with halogenic compounds can improve its ability to capture mercury particles.

The most thoroughly demonstrated treatment to enhance the performance of ACI has been bromination (UNEP 2015). Indian coal is generally characterized as sub-bituminous and bituminous coal (Chandra’ and Chandra 2004; UNEP 2014; Sloss 2015). ACI is one of the appropriate technological methods for Indian power plants because the use of carbon particles after chemical treatment, such as halogen addition, influences the removal of mercury particles from low-rank bituminous, and sub-bituminous coal (Zykov and Anichkov 2014). Some studies on Indian CFPPs had noted the presence of unburnt carbon in fly ash (Sloss 2015). The use of bromine together with this unburnt carbon in fly ash has been suggested to be used as an inherent sorbent to capture mercury (Sloss 2015). If it works, the application of bromine at older CFPPs could enhance the capture of mercury up to 70% without the addition of FGD or SCR, and with minimum capital and operational cost (Sloss 2015).

In recent years, several studies have been carried out to understand the achievable mercury removal efficiencies of air pollution control devices in CFPPs. Bandyopadhyay recommended the installation of Multi Pollution Control Technologies (MPCTs) that can remove most of the pollutants from the CFPP, which the author argued to be more economical than introducing separate technologies for the removal of each pollutant. Bandyopadhyay suggested that MPCTs are a better Indian choice because they consume less water than limestone wet scrubbers and controls more than 90% of the mercury emissions (Bandyopadhyay 2017).

Best available practices/techniques

Efficiency improvements are cost-effective methods to achieve significant mercury reduction until emission control technologies become more common (Nalbandian-Sugden 2015; Sloss 2015). An efficient CFPP emits fewer units of mercury than a less efficient CFPP because the CFPP consumes fewer amounts of coal to produce the same amount of energy. Efficiency improvements give economic benefits with environmental advantages. It has been estimated that the improvement of efficiency in CFPPs would assist India to reduce about 7% of mercury emissions (Giang et al. 2015). Thus, CFPPs could improve their coal combustion efficiency by upgrading burners and equipment, optimizing combustion, proper operation and maintenance, minimizing short cycle and air leakages, and other measures.

India is moving towards increasing the efficiency of the CFPPs by upgrading their equipment and conducting regular systematic performance monitoring, which also supports the reduction of toxicants (Sloss 2012b; Swain 2017). India has been running a renovation and modernization (R&M) programme for existing CFPPs to increase or maintain their efficiency. The main objective of the R&M programme is to equip the CFPPs with the latest technology, equipment, and systems to improve their efficiency and reliability while reducing operation and maintenance requirements (Larson 2019). A joint endeavour between India’s Central Electricity Authority and Japan’s Coal Energy Centre has been supporting the R&M programme by sharing technical expertise and providing solutions for techno-economic problems (CEA 2010). Recently they have agreed to expand their scope of activities to new CFPPs for raising efficiency and maintaining environmental standards (CEA 2010; JCOAL 2019).

Most of the conventional CFPPs use sub-critical pulverized technology; its average power generation efficiency lies in 25% to 35%, which means that the emission of toxicants from these CFPPs is high (Neha 2017). Recent government strategies to improve CFPPs efficiency also aim to replace old inefficient plants with supercritical and ultra-supercritical plants (The World Bank 2008), which provide 37% to 44% and 45% to 60% efficiency, respectively. In addition, a few CFPPS in India has been using Circulating Fluidized Bed technology, which is considered as appropriate for low-rank coal such as that used in India (The World Bank 2008). It can effectively burn coal with ash content of up to 70% (Biswas et al. 2000).

India is also attempting to introduce an integrated gasification combined cycle (IGCC) technology. IGCC has the potential to achieve higher energy generation efficiency than pulverized coal plants, approximately 44–48% (Reddy et al. 2021). With the increase in supercritical plants, the electricity production efficiency should increase. Overall, the coal sector in India is promoting more efficient and cleaner technologies in thermal power generation. Yet, some constraints have been reported in bringing Indian CFPPs closer to international emission standards(Henderson 2015). To operate the CFPPs with higher efficiency, it is necessary to ensure a consistent coal quality, and to have a robust programme of monitoring and maintenance (Henderson 2015).

Coal washing

Coal washing or beneficiation improves coal quality by reducing the extraneous matter or reducing the associated ash, or both (Burnard and Bhattacharya 2011). Post-mining, stones are separated from the coal ore, the ore is then crushed and screened, and then undergoes the process of coal washing (ORF Policy Brief 2017). In 2014, the government issued a notification that state CFPPs of 100 MW capacity or above, located 500 to 749 km from coal mine pit-heads, must utilize raw, blended, or beneficiated coal with an ash content of 34% or less (ORF Policy Brief 2017). Indian coals typically have an ash content of over 40%. So, Coal India Ltd. decided to construct new washeries, including for the processing of coking and non-coking coal (Kumar 2018). Increasing coal washing in India would likely reduce atmospheric emissions of all pollutants, increase efficiency and reduce coal consumption.

In May 2020, the government amended the 2014 notification on coal beneficiation and allowed CFPPs to use unwashed low-grade Indian coal, irrespective of the distance from the mine (Ministry of Environment Forest and Climate Change 2020). It was considered that washeries were also causing pollution. Through this amendment, the production of fly ash waste would be in one place only (at the CFPP) allowing for an easier handling of waste. In addition, the introduction of new emissions standards and improving the efficiency of power plants might equip power plants to deal with potential problems due to the use of unwashed coal. But on the other hand, the high percent of ash in coal reduces the performance CFPPs. So, a large amount of coal has to be burnt to produce a given quality, which will probably increase the emissions. Moreover, the presence of ash in coal increases scheduled and unscheduled maintenance (ORF Policy Brief 2017). The highly erosive ash components will impact the power plant components as they contribute to excessive wear on the ductwork, which might reduce the CFPPs life (Das et al. 2006; Wiatros-Motyka 2019). More studies may be required to find the more appropriate method for Indian coal, considering the environmental and technical costs of coal washing compared to a business-as-usual CFPP operation without coal washing.

Alternative measures: thrust on renewable sources of energy

India’s energy sector is undergoing a transition from coal to renewable energy. Renewable power is becoming increasingly cheaper than fossil fuel-based power (IRENA 2020). Increased generation of renewable power will reduce the demand on coal-based energy generation and would mitigate emissions of mercury as well as other pollutants. Renewable energy costs have fallen sharply over the past decade, driven by improving technologies, competitive supply chains, reduction in tariffs, and growing developer experience (IRENA 2020). In India, the share of non-fossil fuel-based sources in installed capacity of electricity generation increased from 30.5% in March 2015 to 37.7% in May 2020 (PIB 2020). Currently, India has installed renewables for a capacity of 95.66 GW (Ministry of New and Renewable Energy 2021b). A recent report says, renewable energy has a share of 25.24% in the total installed generation capacity in the country (News on Air 2021; Ministry of New and Renewable Energy 2021a). In addition, the Indian government has set a target of 175 GW renewable power installed capacity by the end of 2022 and 500 GW by 2030 (Ministry of New and Renewable Energy 2021a).

The last few years have witnessed a slowdown in the rate of growth of coal-fired capacity addition and a rise in the share of renewable energy (Srinivasan et al. 2018). However, this does not imply that India will stop coal combustion soon. Despite a decline in the growth of the coal-power sector over the past few years, India remains the second-largest coal producer and consumer globally. According to the International Energy Agency, India's energy demand will increase more than that of any other country over the next two decades (PTI 2021). This would need installation of additional power generation capacity. The Central Electricity Authority is projecting to increase the coal-fired capacity by 2030 (Shah 2021b). As per the draft of National Electric Policy 2021, the government is seeking to develop new CFPPs to meet the energy demands (Varadhan 2021). Thus, the transition from coal is a complicated phenomenon. An increase in renewable energy generation will probably reduce the rate of increase of mercury emissions compared to a scenario where expansion was completely through CFPPs, if CFPPs continue to be constructed and operated. However, with the environmental performance of CFPPs expected to increase, it may well be possible to achieve a net reduction in mercury emissions if APCDs are installed progressively and renewables employed aggressively.

Discussion

Current information suggests that implementation of new mercury emission norms may not be enough a force driving actions from CFPPs. But it may still serve as a caution for plant operators to not slack in their emissions controls. Updating of CFPPs to raise their energy efficiency, coal blending and washing, and deployment of new APCDs may facilitate the reduction of mercury emissions. However, for all these measures to have a favourable outcome, some challenges still need to be overcome. Most Indian CFPPs are running below their designed efficiency even as the activities of CFPPs upgradation are in progress. Some old CFPPs are reported to be not fitted with any APCDs (Sloss 2015). Pollution control technologies particularly, dedicated mercury control technologies, are expensive and take time to install. Still, according to some studies the cost of control of the APCDs are lesser when compared to the social and health benefits (Srinivasan et al. 2018). Focus on multi-pollutant control systems may be the most optimal long term solution to mercury emissions problem. The use of ACI or addition of bromine to facilitate cost-effective reduction of mercury may also be considered an interim method to quickly and economically reduce mercury from older units (Sloss 2015).

The existence of clauses in regulations allows CFPPs to adopt lenient strategies in emissions regulations. Instead of a timely implementation of emission norms, giving further extension to CFPPs that have not made adequate progress till date would undermine efforts on mercury emission reduction. A penalty for non-compliance might encourage CFPPs to continue their operations that could pose further risk to the environment. The recent extension in the deadline for implementing emission norms may facilitate procrastination by CFPPs in adopting emission control technologies. Results from some studies show that installing additional pollution control technologies is not required for mercury control in India because the average concentration of mercury in flue gas is lower than stipulated in the new emission standards. All these undermine all efforts to reduce the emission of mercury into the air from a major contributor.

The impact of current emissions norms might become negligible in the future, as increased coal demand could increase atmospheric mercury emissions unless concrete and effective technological measures are used. Despite the growing importance of renewables in the Indian power sector, the country’s dependency on fossil fuels is not decreasing (Yang and Urpelainen 2019). One immediate and practical solution could also be to prioritize installation of control technologies in selected CFPPs informed by modelling of mercury emissions and deposition. Overall, a multi-pronged approach to improve energy efficiency, implementation of APCDs, and aggressive pursuit of renewables, aided by strict time-bound emission norms, will be required to reduce the amount of mercury emitted to the environment in India.

Biographies

Alphin Joy

Alphin Joy is a Senior Research Associate at CUTS International, a global policy and advocacy think-tank. His work involves analyses and interpretation of policies related to environmental and human health impacts of anthropogenic activities, specifically chemical pollution. Before joining CUTS, he worked at the Indian Institute of Technology Hyderabad as Junior Research Fellow. He has a master’s degree in International Relations and Political Science, and a bachelor’s degree in International Relations, both from the Central University of Kerala. His master’s dissertation was on India’s maritime security concerns in the Indian Ocean. Prior, he worked on regional economic diplomacy in relation to India as a donor in South Asia. His primary interests are international relations, international environmental policies, and environmental security.

Asif Qureshi

Asif Qureshi is an Associate Professor at IIT Hyderabad. He has D.Sc. in Environmental Science from the Swiss Federal Institute of Technology (ETH) Zürich. The overarching theme of his research is to understand how chemical and biological agents may impact present and future environmental health. Impacts are understood under present scenario and future scenarios. Scientific methods are used to provide knowledge that may help inform policy making. He has worked for more than ten years on issues related to global mercury pollution, environmental modeling, and human exposure.

Author contributions

AJ and AQ conceived the idea. AJ conducted research, AJ and AQ interpreted the work and wrote the manuscript. Both authors read and approved the final manuscript.

Declarations

Competing interests

The authors declare that they have no competing interests.