coal power plants as source of water and air pollution

8/7/2019 Coal Power Plants as Source of Water and Air Pollution

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By

Loretta C. Romero



y Power generating units aremega projects

y Require huge capital

investmenty Require natural resources

like, fossil fuels

y Large amount of water

y Changes the local eco system

y Huge Impacts on theEnvironment and Health



y More than half of the electricity generated in the worldis by using coal as the primary fuel.

y The function of the coal fired thermal power plant is to

convert the energy available in the coal to Electricity.y Coal power plants work by using several steps to

convert stored energy in coal to usable electricity thatwe find in our home that powers our lights, computers,

and sometimes, back into heat for our homes.



The conversion from coal to electricity takes place inthree stages.

Stage 1

y The first conversion of energy takes place in the boiler.Coal is burnt in the boiler furnace to produce heat.

Carbon in the coal and Oxygen in the air combine toproduce Carbon Dioxide and heat.

y



Stage 2

y The second stage is the thermodynamic process.

y The heat from combustion of the coal boils waterin the boiler to produce steam. In modern powerplant, boilers produce steam at a high pressure and

temperature.y The steam is then piped to a turbine.

y The high pressure steam impinges and expandsacross a number of sets of blades in the turbine.

y The impulse and the thrust created rotates theturbine.

y The steam is then condensed and pumped back

into the boiler to repeat the cycle.



Stage 3

y In the third stage, rotation of the turbine rotates thegenerator rotor to produce electricity based of Faradays Principle of electromagnetic induction.



Though each plant is unique in itself in terms of specificfeatures and functionalities, still there is a broadoutline to which all thermal power plants confirm to.There are four main circuits in any thermal power

plant and these are:

1. Coal & Ash Circuit this circuit deals mainly withfeeding the boiler with coal for combustion purposesand taking care of the ash that is generated during the

combustion process and includes equipment andparaphernalia that is used to handle the transfer andstorage of coal and ash.



2. Air & Gas Circuit we know that air is one of the main

components of the fire triangle and hence necessary for combustion. Since lots of coal is burnt inside theboiler it needs a sufficient quantity of air which issupplied using either forced draught or induced

draught fans. The exhaust gases from the combustionare in turn used to heat the ingoing air through a heatexchanger before being let off in the atmosphere. Theequipment which handles all these processes fall

under this circuit.



3. Feed Water & Steam Circuit this section deals withsupplying of steam generated from the boiler to the

turbines and to handle the outgoing steam from theturbine by cooling it to form water in the condenser sothat it can be reused in the boiler plus making goodany losses due to evaporation etc.

4. Cooling Water Circuit this part of the thermalpower plant deals with handling of the cooling waterrequired in the system. Since the amount of waterrequired to cool the outgoing steam from the boiler issubstantial, it is either taken from a nearby watersource such as a river, or it is done through evaporationif the quantity of cooling water available is limited.



y Around 2 million tons of coal will be required each year toproduce the continuous power.

y Coal combustion in the boiler requires air. Around 1.6million cubic meter of air in an hour is delivered by air fans

into the furnace.y The ash produced from this combustion is around 200,000

tons per year.

y Electrostatic precipitators capture almost all of this ashwithout dispersing this to the atmosphere. Pollutants fromcoal power plants like carbon dioxide, sulphur dioxide, andnitrogen oxide can also affect the environment. Thermal

power plants are the biggest producers of Carbon Dioxide.

y



y The boiler for typical 500 MW units produces around1600 tons per hour of steam at a temperature of 540 to600 degrees Centigrade. The steam pressures is in therange of 200 bar. The boiler materials are designed to

withstand these conditions with special considerationfor operational safety.

y Heat transfer from the hot combustion gases to thewater in the boiler takes place due to Radiation and

convection.



y The Electrical generators carry very large electric currentsthat produce heat and are be cooled by Hydrogen andwater.

y The steam leaving the turbine is condensed and the water

is pumped back for reuse in the boiler. To condense all thesteam it will require around 50,000 cubic meter per hour of cooling water to be circulated from lakes, rivers or the sea.The water is returned to the source with only an increase of 3 to 4 degrees centigrade to prevent any effect to the

environment.y Apart from the cooling water the power plant also requires

around 400 cubic meter per day of fresh water for makingup the losses in the water steam cycle.



By products of Coal Power Plants causes

water and air pollution with directimpact on the environment and onhuman health



AirQuality y Around the coal based plants the

ambient concentrations of SulphurDioxide, Oxides of Nitrogen and SPM arehigh.

y

Epidemiological Studies have shown thatof the area surrounding coal basedthermal plants, population living within a2 -5 km radius of the plant suffers fromrespiratory disorders .

y Two other gases, carbon dioxide and

ozone are emitted. The high amount of carbon dioxide emission from thermalpower plants contribute to globalwarming leading to climate change issignificant Ground level ozone, which isformed due to photolytic reactions of NO

xand its impacts are under study



y Fly ash contains a toxic brew of dangerous chemicals and is the largestcontributor to mercury pollution



y Composition of Fly ash

It contains as main chemical components SiO2(Silicone

Dioxide) (51.4 wt%), Al2O3 (Aluminum Oxide)(22.1 wt%)

and Fe2O3( Iron Oxide) (17.2 wt%; ignited weight basis).As commonly observed, many toxic elements andheavy metals are highly enriched in the fly ash relativeto the original coal. For example, considerableamounts of Be(Beryllium) (16.4 ppm), Cu( Copper) (106ppm), Zn (zinc)(578 ppm), As(Arsenic) (40.4 ppm), Cd( Cadmium) (2.6 ppm), Hg (Mercury )(18 ppm), Pb( Lead) (71ppm), and U (21.8 ppm) is found in Fly ash.



y Water slurry is used to take the ash from the power plant tothe ash pond for disposal.

y Water slowly seeps into the ground while carrying with itthe ash leachate. Water may contain harmful heavy metals

like boron, which have a tendency to leach out over aperiod of time.

y When fly ash comes into contact with water, leaches intogroundwater supplies which get polluted and unsuitablefor domestic use.

y The release of ash pond decant into the local water bodies-water dries up, dust nuisance, increases turbidity, decreasesprimary productivity, affects fishes and other aquatic biota



y Large amount of land is usedto dispose flyash from the coalbased plants

y Due to this there is change innatural soil properties. Itbecomes more alkaline due tothe alkaline nature of fly ash.



y The exposure of employees to high noiselevels is very high

y Increased transportationactivities due to theoperation of the powerplants lead to increase in

noise levels in theadjacent localities.



y Alkali and metal processing, incineration of coal,medical and other waste, mining of gold and mercury contribute greatly to mercury concentrations in someareas, but atmospheric deposition is the dominant

source of mercury over most of the landscape.y Natural sources of atmospheric mercury include

volcanoes, geologic deposits of mercury, andvolatilization from the ocean. Although all rocks,

sediments, water, and soils naturally contain small butvarying amounts of mercury, scientists have foundsome local mineral occurrences and thermal springsthat are naturally high in mercury.



y Each year power plants and chemical facilities createmany tons of mercury pollution, which makes its way into our homes and bodies in fish.

y Two of the biggest sources of mercury pollution arechlorine chemical plants and coal-fired power plants.Chlorine plants, which use massive quantities of mercury to extract chlorine from salt, "lose" dozens of tons of mercury each year; power plants emit around

50 tons of mercury pollution annually. Coal is naturally contaminated with mercury, and when it is burned togenerate electricity, mercury is released into the airthrough the smokestacks.



y The cycle of mercury in nature is complex. This illustrationsummarizes how methyl mercury accumulates at the higher levels of the food chain and becomes concentrated in fish and animals that eatfish.

y Methylmercury in the water and sediment is taken up by tiny animalsand plants known as plankton.

y Minnows and juvenile fish eat large quantities of plankton over time.y Larger predatory fish consume many smaller fish, accumulating

methylmercury in their tissues. The older and larger the fish, thegreater the potential for high mercury levels in their bodies.

y Fish are caught and eaten by humans and animals, causingmethylmercury to accumulate in human tissues.

y Most people are exposed to mercury by eating fish containing mercury.There is no method of cooking or cleaning them that will reduce theamount of mercury in a meal.



What factors affect the methylation?

Methylation is a product of complex processes that move and transform mercury.Atmospheric deposition contains the three principal forms of mercury, although

inorganic divalent mercury (HgII) is the dominant form. Once in surface water,

mercury enters a complex cycle in which one form can be converted to another.

Mercury attached to particles can settle onto the sediments where it can diffuse into

the water column, be resuspended, be buried by other sediments, or be methylated.

Methylmercury can enter the food chain, or it can be released back to the

atmosphere by volatilization.

The concentration of dissolved organic carbon (DOC) and pH have a strong effect

on the ultimate fate of mercury in an ecosystem. Studies have shown that for the

same species of fish taken from the same region, increasing the acidity of the water

(decreasing pH) and/or the DOC content generally results in higher mercury levels

in fish, an indicator of greater net methylation. Higher acidity and DOC levels

enhance the mobility of mercury in the environment, thus making it more likely to

enter the food chain.

Mercury and methylmercury exposure to sunlight (specifically ultra-violet light) has

an overall detoxifying effect. Sunlight can break down methylmercury to Hg(II) or

Hg(0), which can leave the aquatic environment and reenter the atmosphere as a

gas.



Air borne mercury is highly toxic when inhaled. How does it get in the air?

y Metallic mercury slowly evaporates when exposed to the air. The air in aroom can reach unhealthy levels just from the mercury in a brokenthermometer;

y Mercury may be released into the air when coal, oil, or wood are burnedas fuel or when mercury-containing wastes are incinerated. The resultingmercury concentrations in outdoor air are usually low and of little directconcern. However, mercury in the air can fall to the ground with rain andsnow, landing on soil or in bodies of water, causing contamination.Lakes and rivers are also contaminated when there is a direct discharge

of mercury-laden industrial or municipal waste into the water.y When mercury enters bodies of water, biological processes transform it

to methylmercury, a highly toxic and bioaccumulative form. Fish canabsorb methylmercury from their food and directly from water as itpasses over their gills.



y Toxicology:

y How Mercury Harms Humans Elemental (metallic) mercury and all of itscompounds are toxic, exposure to excessive levels can permanently damage orfatally injure the brain and kidneys.

y Elemental mercury can also be absorbed through the skin and cause allergicreactions. Ingestion of inorganic mercury compounds can cause severe renal

and gastrointestinal damage.y Organic compounds of mercury such as methyl mercury are considered the

most toxic forms of the element. Exposures to very small amounts of thesecompounds can result in devastating neurological damage and death.

y For fetuses, infants and children, the primary health effects of mercury are onneurological development.

y Even low levels of mercury exposure such as result from mother's consumptionmethyl mercury in dietary sources can adversely affect the brain and nervoussystem.

y Impacts on memory, attention, language and other skills have been found inchildren exposed to moderate levels in the womb.



yy The most massiveThe most massive pollution problem to

strike Japan in the post WWII period.

y A neurological syndrome caused by methyl

m

ethylmercury mercury in the industrial wastewater.

y Continued from 1932 to 1968 (36 years)

y 2 cities (Minamata and Niigata wereaffected in Japan)



y Minamata disease was firstdiscovered in Minamata city in Japanin 1956. It was caused by the releaseof methyl mercury in the industrialWaste water from the ChissoCorporation's chemical factory,

which continued from 1932 to 1968.This highly toxic chemicalbioaccumulated in shellfish and fishinMinamata Bay and the ShiranuiSea, which when eaten by the localpopulace resulted in mercury poisoning. While cat, dog, pig and

human deaths continued over morethan 30 years, the government andcompany did little to prevent thepollution.



y Minamata disease sometimesreferred to as Chisso-Minamata

disease is a neurological syndromecaused by severe mercury poisoning. Symptoms includeataxia, numbness in the hands and

feet, general muscle weakness,narrowing of the field of vision anddamage to hearing and speech. Inextreme cases, insanity, paralysis,coma and death follow within

weeks of the onset of symptoms. A congenital form of the disease canalso affect fetuses in the womb.



y As of March 2001, 2,265victims had been officially recognised (1,784 of whomhad died)and over 10,000 hadreceived financial

compensation from Chisso,lawsuits and claims forcompensation continue tothis day.

y A memorial service was held

at the Minamata DiseaseMunicipal Museum on 1 May 2006 to mark 50 years sincethe official discovery of thedisease.

coal power plants as source of water and air pollution

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