Impact of coal based thermal power plant on environment and its mitigation measure

AbstractIndia is the world’s fourth largest economy and has a fast growing energy market. India’s current

power capacity is 30% short of demand. Coal and petroleum are the primary sources of energy.

High ash content in Indian coal and inefficient combustion technologies contribute to India’s

emission of air particulate matter and other trace gases, including gases that are responsible for

the greenhouse Due to thermal combustion of coal produces radionuclide and a portion of

radionuclide’s produces from the ash this create health hazards. Due to increasing the demand of

energy use of coal is increasing significantly so we can mitigate the pollution by using several

alternatives like for removal of fly ash, using fly ash for making bricks, cement, distemper

rceramics,fetilizerand use in road construction .therefore by utililizing fly ash we can reduces the

health hazards.

Key words-Coal, Fly ash, Radionuclide, Thermal power, Green house gas

1. Introduction

Coal is the only natural resource and fossil fuel available in abundance in India. Consequently, It

is used widely as a thermal energy source and also as fuel for thermal power plants producing

electricity. Power generation in India has increased manifold in the recent decades to meet the

demand of the increasing population. Generating capacity has grown many times from 1362MW

in 1947 to 147,403MW (as on December 2008). India has about 90,000 MWe installed capacity

for electricity generation, of which more than 70% is produced by coal- based thermal power

plants. The only fossil fuel available in abundance is coal, and hence its usage will keep growing

for another 2–3 decades at least till nuclear power makes a significant contribution. The coal

available in India is of poor quality, with very high ash content and low calorific value, and most

of the coal mines are located in the eastern part of the country. Whatever good quality coal

available is used by the metallurgical industry, like steel plants. The coal supplied to power

plants is of the worst quality. Some of the coal mines are owned by private companies, and they

do not wish to invest on quality improvement. Combustion process converts coal into useful heat

energy, but it is also a part of the process that produce greatest environmental and health

concerns. Combustion of coal at thermal power plants emits mainly carbon dioxide (CO2),

sulphur oxides (SOx), nitrogen oxides (NOx), CFCs other trace gases and air borne inorganic

particulates, such as fly ash and suspended particulate matter (SPM). CO2, NOx and CFCs are

green house gases (GHGs) High ash content in Indian coal and inefficient combustion

technologies contribute to India’s emission of air particulate matter and other trace gases,

including gases that are responsible for the greenhouse effect.

2. Problems associated with CO2 increase in atmosphere

CO2 produced in combustion is perhaps not strictly a pollutant (being a natural product of all

combustion), nonetheless it is of great concern in view of its impact on global warming. Carbon

dioxide is a stable molecule with less than 10 years average residence time is 3 years in the

troposphere though its residence time is over 100 years in the atmosphere, and its present

concentration in the atmosphere is increasing at an astonishing rate of 0.4% per year. Electricity

has been a preferred form for energy consumption and has consistently registered a higher

growth rate than other forms of energy. India is a developing country with over a billion

population and immense natural resources with total surface area of 3,287,590 sq. km and a huge

land area of 2,973,190 sq. km. Increased consumption of electric power is more intimately bound

up with economic development on the one hand and increased emission of pollutants on the

other hand. Establishment of new industries, plants, commercial complexes and expansion of the

capacity for consumer goods industries to feed its ever increasing population has led to a

considerable increase in the consumption of electricity in India and, consequently, the emission

levels of CO2. Based on their studies in the northern hemisphere, Dunn and Flavin stated that

carbon dioxide, which is released into the atmosphere from the burning of fossil fuels, is the

single most important greenhouse gas contributing to the ‘‘anthropogenic forcing of climate

change’’. Thus, they conclude the share of CO2 in warming is expected to rise from slightly more

than half today to around 3/4th by 2100 and further stated that the average global surface

temperature would be raised more during the 20th century than during any other century in the

last 1000 years. Carbon dioxide comprises about 0.03% of the earth’s atmospheric volume, but

due to the combustion of fossil fuels and deforestation, this percentage has increased by about

25% since preindustrial times. Each year about 5 Gt of carbon is released into the atmosphere

due to fossil fuel combustion. The average concentration of CO2 in the atmosphere has already

reached 358 ppm by volume (ppmv), compared to the pre-industrial level of 280 ppmv.

Scientists project that excessive CO2 emissions into the atmosphere will increase the earth’s

surface temperature In most developing countries, CO2 emissions are between 0.3 and 0.6 tons of

carbon per capita per year. The relative rate of CO2 emission increase in developing countries has

been much larger during the last few decades (about 5% per year in developing regions in

contrast to 1% per year in industrial regions during the last decades) Fast accumulation of carbon

dioxide in the atmosphere can evidently affect the climate of earth rather quickly by warming the

earth surface. This effect is associated with the absorption of long wavelength radiation much

more by CO2 than other GHGs. In particular, the atmosphere of the northern hemisphere will be

warmer because of anthropogenic carbon dioxide when this contribution will have reached

several billion tons, corresponding to a60 ppm increase in concentration from now, such an

increase could take place by the year 2010. The Intergovernmental Panel on Climate Change

(IPCC) suggests that the global mean surface temperature of the earth has increased by between

0.3° and 0.6° C since the late 19th century. Giorgi and Hewitson concluded that a doubling of

CO2 would increase the temperature by 2–4° C and decrease rainfall by 10–20%. Carbon dioxide

has already risen by 30% since the industrial era began. The global atmosphere traps an

increasing amount of heat due to the increased concentration of CO2, and thus, higher

temperatures result globally. This change in atmospheric temperature is of concern since even an

increase of a few degrees would lead to severe regional effects, such as prolonged droughts, crop

failure, change in cropping pattern, vegetative production with increased desertification, polar ice

might partially melt, resulting in ocean flooding and submergence of major portions of low lying

islands and coastal areas. Problems like global warming, climate change, emergence of natural

hazards like flooding and change in sea levels.

3. Problems associated of increasing fly ash

India has about 211 billion tons of coal reserves, which is known to be the largest resource of

energy and presently 240MT of coal is being used annually to meet the Nation’s electricity

demand. In terms of energy, India stands at world sixth position accounting 3.5% of the world

commercial energy demand in 2001, but the electricity generation yet not completely fulfilled the

present requirement. Though nuclear power programmed envisaged for generation of

20,000MWof nuclear energy by the year 2020, India do not have option in the foreseeable future,

except the fossil fuel mainly based on coal sources. The rate of annual increase in power

generation in India is 5%. And at this rate the annual power generation by the year 2020 is

expected to be 180,000MW, which may release about 190MT of CCRs per annum. However, to

achieve sustainable development the Nation may have to generate at least 260,000MW of power

(i.e. 10% increases in rate of annual electricity generation) by the year 2020 and as consequence

273MT of CCRs is expected to be released. Keeping in view of the formidable future problems

due to these huge quantity of CCRs to achieve Environmental Sound Management, it is very

crucial time for confidence building on CCRs utilization and increase in acceptability of CCRs

based products among the end users Environmental pollution by the coal based thermal power

plants all over the world is cited to be one of the major sources of pollution affecting the general

aesthetics of environment in terms of land use, health hazards and air, soil and water in particular

and thus leads to environmental dangers. Coal combustion residues (CCRs) are a collective term

referring to the residues produced during the combustion of coal regardless of ultimate utilization

or disposal. It includes fly ash, bottom ash, boiler slag, and fluidized bed combustion ash and

other solid fine particles(Asokan,2003;Keefer,1993) As per the ASTM standards, in India

bituminous and sub-bituminous coal results in class ‘F’ash and lignite coal produces class‘C’ ash

having high degree of self-hardening capacity. In India, presently coal based thermal power

plants are releasing 105MT of CCRs which possess major environmental problems (Kumar and

Mathur, 2004; Sharma et al., 2003).Presently from all these thermal power plants, dry fly ash has

been collected through Electrostatic Precipitator (ESP) in dry condition as well as pond ash from

ash ponds in semi-wet condition. In India most of the thermal power plants do not have the

facility for automatic dry ash collection system. Commonly both fly ash and bottom ash together

are discharged as slurry to the ash pond/lagoon these affect on environment, economy, and social

factor.

4. Problems associated with radionuclide increase in atmosphere coal combustion

Coal, like most materials found in nature, contains also natural radionuclides. The levels of

natural radionuclides in a geological formation depend on its composition and geological history.

In the production of electric power, coal is burned in a furnace operating at temperatures of up to

1700°C. In the combustion process, volatile radionuclide’s such as Pb210 and Po210 are partly

released in the flue gases and escape to the atmosphere. A significant fraction of the radioactivity

is also retained in the bottom ash or slag .The greatest part of the radioactivity in coal remains

with the ash but some of the fly ash from coal-fired power plants escapes into the atmosphere.

Air pollution in the vicinity of a coal fired thermal power station affects soil, water, vegetation,

the whole ecosystem and human health. Air pollution in the vicinity of a coal fired thermal

power station affects soil, water, vegetation, the whole ecosystem and human health.

"Environmental impact of coal utilization in thermal power plant" notes that "Radon is a

colorless, odorless but noble gas, which is radioactive and ubiquitously present. It poses grave

health hazards not only to uranium miners but also people living in normal houses and buildings

and at work place like coal mines, cement industry, thermal power plants etc. Coal, a naturally

occurring fossil fuel is burnt in conventional power plants to meet out about 72% of the

electricity needs in our country. It was lesser known hitherto until recently that the fly ash which

is a byproduct of burnt coal is a potential radioactive air pollutant and it modifies radiation

exposure.

6. Fly ash mitigation measure

Fly ash is fine glass powder, the particles of which are generally spherical in shape and range in

size from 0.5 to 100 micron. Fly ash is classified into two types according to the type of coal

used. Anthracite and bituminous coal produces fly ash classified as class F. Class C fly ash is

produced by burning lignite or sub-bituminous coal. Class C fly ash has self-cementing

properties. . Fly ash emissions from a variety of coal combustion units show a wide range of

composition. All elements below atomic number 92 are present in coal ash Particulate matter

(PM) considered as a source of air pollution constitutes fly ash. The fine particles of fly ash reach

the pulmonary region of the lungs and remain there for long periods of time; they behave like

cumulative poisons. The submicron particles enter deeper into the lungs and are deposited on the

alveolar walls where the metals could be transferred to the blood plasma across the cell

membrane Fly ash can be disposed-off in a dry or wet state. Studies show that wet disposal of

this waste does not protect the environment from migration of metal into the soil1. Heavy metals

cannot be degraded biologically into harmless products like other organic waste. Studies also

show that coal ash satisfies the criteria for landfill disposal, according to the Environmental

Agency of Japan 2. According to the hazardous waste management and handling rule of 1989,

fly ash is considered as non-hazardous. With the present practice of fly-ash disposal in ash ponds

(generally in the form of slurry), the total land required for ash disposal would be about 82,200

ha by the year 2020 at an estimated 0.6 ha per MW. Fly ash can be treated as a by-product rather

than waste.

i) Fly ash bricks

The Central Fuel Research Institute, Dhanbad has developed a technology for the utilization of

fly ash for the manufacture of building bricks. Fly ash bricks have a number of advantages over

the conventional burnt clay bricks. Unglazed tiles for use on footpaths can also be made from it.

Awareness among the public is required and the Government has to provide special incentives

for this purpose.

Six mechanized fly ash brick manufacturing units at Korba are producing about 60000 bricks per

day. In addition to this, two mechanized fly ash brick manufacturing units have been set up by

private entrepreneurs also at Korba, the total production being about 30000 bricks/day. Apart

from this about 23 entrepreneurs have registered in DTIC proposals for establishing ash brick

units. To give impetus to ash brick manufacturing, District Mining Officer, who is also the Nodal

Officer for fly ash utilization, is ensuring strict compliance of certain vital instructions issued in

connection with conventional brick making by MoEF i.e. mixing a minimum of 25% fly ash with

clay and fixed chimney in place of moving kilns.

ii) Fly ash in manufacture of cement

Fly ash is suitable for use as pozzolana. In the presence of moisture, it reacts chemically

with calcium hydroxide and CO2 present in the environment attack the free lime causing

deterioration of the concrete. A cement technologist observed that the reactive elements

present in fly ash convert the problematic free lime into durable concrete. The difference

between fly ash and Portland cement becomes apparent under a microscope. Fly ash

particles are almost totally spherical in shape, allowing them to flow and blend freely in

mixtures. This property makes fly ash a desirable admixture for concrete.

Current installed capacity of Indian cement industry is 110 MT per annum. Further, it is an

established fact that the mortar and the concrete with PPC perform better on strength as

well as durability parameters. As per the specifications of Bureau of Indian Standards fly

ash upto 35% can be used in manufacture of PPC, while worldwide there are examples of

countries that permit up to 55% utilization of fly ash in PPC production. Keeping in view

the technical advantages use of PPC be preferred on OPC, except in cases where in early

strength is very essential. Setting aside 25% of cement production for OPC for such

applications, the balance 75% can be PPC with an average fly ash content of 30%. It would

consume around 25 MT fly ash, replacing same amount of cement clinker and resulting in

net saving Rs. 2500 crores.

iii) Fly ash in distemper

Distemper manufactured with fly ash as a replacement for white cement has been used in several

buildings in Neyveli, Tamil Nadu, in the interior surfaces and the performance is satisfactory.

The cost of production will only be 50% that of commercial distemper.

iv) Fly ash-based ceramics

The National Metallurgical Laboratory, Jamshedpur has developed a process to produce

ceramics from fly ash having superior resistance to abrasion.

v) Fly ash as fertilizer

Fly ash provides the uptake of vital nutrients/minerals (Ca, Mg, Fe, Zn, Mo, S and Se) by crops

and vegetation, and can be considered as a potential growth improver. It serves as a good

fertilizer. Because It can be a soil modifier and enhance its moisture retaining capacity and fertility. It

improves the plant's water and nutrient uptake, helps in the development of roots and soil binding Use of

fly ash in agriculture has also proved to be economically rewarding. The improvement in yield

has been recorded with fly ash doses varying from 20 tone / hectare to 100 tone / hectare. On an

average 20-30% yield increase has been observed. Out of 150 million hectare of land under

cultivation, 10 million hectares of land can safely be taken up for application of fly ash per year.

Taking a moderate fly ash dose of 20 mt per hectare it would consume 200 million tone flyash

per year. This is more than the annual availability of fly ash, therefore the shortfalls would be

met from accumulated 1500 million tonne stock of fly ash (available in ash ponds). The fly ash

treated fields would give additional yield of 5 million tone food grains per year valued at about

Rs. 3000 crores.

vi) Fly ash in road construction

The use of fly ash in large quantities making the road base and surfacing can result in low value–

high volume utilization.

3 technology demonstration projects at New Delhi, Dadri (U.P.) and Raichur (Karnataka) have

been successfully completed for use of fly ash in road / flyover embankments. Guidelines have

been prepared and approved by Indian Roads Congress (IRC) as national standard. More than 10

multiplier effects have taken place across the country

Nizammuddin Bridge approach road embankment at New Delhi (in flood zone of river Yamuna

vii) Roads and Embankments

Another area that holds potential for utilization of large volumes of fly ash is road and flyover

embankments. Fly ash embankments at Okhla, Hanuman Setu, Second Nizamuddin bridge in

Delhi and roads at Raichur, Calcutta, Dadri etc. have established that on an average Rs. 50 to 75

per MT of earth work cost can be saved by using flyash (in lieu of soil) in such works, primarily

due to reduction in excavation & transportation costs.

7. Mitigation measure of radionuclide

1-The deposited materials like fly ash, bottom slag and their mixtures with gypsum (product of

desulphurization) show slightly enhanced external radiation on the disposal site, but solely on the

bear surface. A dose rate levels approach to the background level at the distance of some metres.

2-The technological improvement such as the dry disposal site for coal ash (instead of direct

inflow of ash slurry into the lake), introduction of a closed circuit of transport water and

introduction of the desulphurization process for stack releases, significantly reduced discharged

radioactivity into the environment. Positive findings of monitoring are reflected consequently in

decreasing trends of environmental contamination and lower environmental impact.

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