India’s INDC in Paris convention pledges an emission intensity reduction by 33-35% of 2005 level, creation of additional carbon sink through additional tree and forest cover, and increase in electricity capacity from non-fossil based fuel resources by 40% by 2030 (INDIA-INDC, 2015). All three pledges and a promise for access to electricity to all, demanded stern actions from electricity sector of India. Presently the sector is dominated by fossil fuel, especially coal. India is the third largest emitter of greenhouse gases in the world although emission per capita of GDP is still low, at one third of world’s average.

Electricity sector, due to its dependent on fossil fuel, is responsible for 37.7% of GHG emission and 47% of CO2 emission (PLANN COMM, 2014) as per 2007 data. India’s per capita consumption is one of the lowest in the world. Around 304 million (24% of global population) people do not have access to electricity.

Country is presently riding on a substantial economic growth which needs infrastructure development and massive increase in electricity generation capacity.

Fig1: Electricity demand of India in New policies scenario by IEA

As clear from the INDC, coal would continue to be primary resource for some time due to its availability and cheap cost (INDIA-INDC, 2015).

Fig 2: INDC projection of India’s electricity generation mix (IEA, 2015)

In INDC scenario, electricity consumption of the country more than doubles to 2550 TWh by 2030 from its 2013 value, and probably this cannot be achieved without coal. Fig 3: Operating load as proportion of design maximum continuous rating (%MCR) (IEA, 2010)

Hence, the strategy adopted to balance the climate goal along with meeting the rising power demand due to factors like economic growth and urbanization, should be to balance fuel mix with increasing renewable gradually, while improving quality of power derived from fossil fuel. Hence, while we build our renewable power capacity for our climate goal, it is also important to simultaneously work on reducing emission in coal based power generation.

Emission intensity of electricity supply in India is relatively high (926 gCO2/kWh in 2012) and average emission intensity of Indian coal based power plant is 1.03 t/MWH(CEA, 2014).

CO2 Mitigation through Efficiency……………

Average efficiency of coal based sub-critical plants are 37.4 % with high load factor (for performing units like that of NTPC) and high availability (CSE, 2015). APEC Energy working group study of 2008 says that for a coal based power station, efficiency improvement of 3% can result into about 9% reduction in CO2 emission (APEC, 2008). IEA study also reaffirms that an efficiency improvement of 1% in a conventional coal fired plant can reduce carbon emission by 3% (IEA, 2014).

Factors influencing efficiency

  • Impact of age –Units which started operation from mid-80s to mid-90s, have crossed more than twenty years. Some of the units are even older as they were taken over from various state electricity boards.

With increasing age, efficiency of the plant gradually decreases as heat rate increases (Efficiency = 860/Heat Rate).

  • Operating condition – Efficiency of a thermal power plant is optimum at full load (APEC, 2008).

Fig 3: Operating load as proportion of design maximum continuous rating (%MCR) (IEA, 2010)

Due to integration issues, absence of resilient grid and tariff issues, many of the plants are run on part load, at times. Thus, efficiency is reduced. Sub-critical plants are most affected as they are designed for base load operation.

Average plant load factor of Indian coal based plant is 67% (2016 data). Due to addition of more renewable to the grid coal plants are running on part load, reducing efficiency and increasing emission.

Improvement in Efficiency……………………..

Use of technology:

  • Supercritical Technology: Supercritical and ultra-supercritical technology coal plants are more efficient. Relation between CO2 emission and technology has been established by studies.

Fig 4: Relation between CO2 emission efficiency and technology (Source: Electricity generation, Facts and Figures, VGB Powertech.)

The supercritical units as of now are having a 5% gain in efficiency (around 15% reduction in CO2 emission as per APEC study). Thereof, new supercritical plants are planned with more improved parameters and each is expected to improve efficiency by 3.7% over conventional existing supercritical plant (around 25% reduction in CO2).

  • Reheat temperature: It has been seen in studies at various places that increasing reheat temperature of sub-critical unit increases efficiency by 0.7%.

In new coal plants adding second reheat stage will increase efficiency by 1% (IEA, 2014), which can be explored in design stage.

Use of high efficiency electrostatic precipitator: In new plants and retrofitting in old plants will help to reduce stack emission, reducing particulate matter.

  • Retrofitting or upgrading old plants with efficient equipment

A study by US Department of Energy (USDOE) published a study result on potential improvements to existing coal fired power plant efficiency.

Table 1:Potential efficiency improvements from measures to increase the efficiency of existing coal fired power plants (IEA, 2015)

According to the above data, it can be seen that with retrofit and upgrade, and overhaul, and following best practices in plant operation and maintenance, a substantial amount of efficiency improvement and hence CO2 emission reduction up to 30% can be achieved.

Government needs to look into such regulation norms on fossil fuel based power stations, and allow R&M for sub-critical plant as capital expenditure to increase efficiency to make its climate target a success.

  • Optimized operation

Restoring the plant to operate near to design conditions will also help in efficiency (APEC, 2008). Wherever renovation and modernization projects for old plants are taken up, it should aim for such operation. Proper overhauling of plants nowadays have become very difficult again due to tariff regulations and overhauling is being completed hurriedly, which is increasing forced outage and efficiency loss.

With technologies like CCS being expensive and still in experimental stage (PLANNCOMM, 2014), for Indian power generators with coal based plants, efficiency improvement is the most cost effective way to reduce CO2 emission.

Along with CO2 emission reduction, improved efficiency of a thermal power plant reduces water consumption as well.

CO2 mitigation through retiring old fleet………

Replacing retiring power stations is another way to curb emission in world scenario.

Fig 4: Age profile of thermal capacity in India (IEA, 2015)

Most of the old coal based power plants in India are of smaller capacity and retiring those, may not add to a large capacity loss. Hence, this of course is a viable option for reducing emission. But since, capacity is low, would not contribute to a substantial reduction, unless sub critical plants of higher capacities like 500 MW of 10-20 years are considered, which may not be a pragmatic solution at this point of time considering the rising demand, with estimated economic growth.

Emission reduction by renewable sources…………

This is of course one measure which is in the top of the agenda list in India nowadays. Most of the power generators in India are already in action to balance their fuel mix with renewables like solar and wind.

 

Challenges for Emission Reduction…………

  • Lack of demand schedule / insufficient loading – Restructuring of power sector, tariff regulation, transmission and distribution loss reduction, are required to increase load factor of thermal plant.
  • Policy / Regulations – Tariff structure presently has no consideration on efficiency based performance. More efficient plants need to get incentive. Policy discourages generators in retrofitting or upgrading as that increases the cost of power and generator is unable to sale power in the face of competition.

Policies like Energy pricing, Coal cess and PAT need to be enforced to aid supercritical plants.

  • Investment – CO2 reduction through efficiency improvement, carbon sink and renewable sources require lot of finance.

Conclusion………

It is possible to achieve emission reduction in coal based plants in Indian electricity sector, while continuing to achieve a balanced fuel mix with increasing share of renewable in future.

Future coal plants with advanced technology and efficiency enhancing measures for old sub-critical plant, together, are quite capable of reducing emission as per climate goal. But a need for policy restructuring and regulatory revision is there.

(Excerpt from a detail study based on similar subject by the author)

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