CoalToElec 18.10.2010

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K. Bhanu Prakash

Coal To Electricity

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Presentation Overview

General statistics of coal based generation

Coal and its issues with generation

Coal handling and transportation

Coal combustion

Chemical Energy to thermal energy

Thermal to mechanical energy

Mechanical to electrical energy

Presentation Overview Page 2

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Coal To Electricity


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Power scenario in India

Date | Title of Presentation Page 4

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Generation


Total Installed Capacity is 156092.91 MW

Thermal Power

Current installed capacity of Thermal Power (as of 12/2008) is93,398.84 MW which is 64.7% of total installed capacity.

Current installed base of Coal Based Thermal Power is 77,458.89MW which comes to 53.3% of total installed base.

Current installed base of Gas Based Thermal Power is 14,734.01 MWwhich is 10.5% of total installed base.

Current installed base of Oil Based Thermal Power is 1,199.75 MWwhich is 0.9% of total installed base.

The state of Maharashtra is the largest producer of thermal power inthe country

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Power generation in the country


The government has estimated that India will require an installed capacity of over

200,000 megawatt (MW) by 2012 to meet the electricity demand, which will be 60percent more of what the country has at present.

At present, about 26 percent of installed power generation capacity in India ishydropower against 50 percent in the 1960s, while around 66 percent is thermalgeneration including gas.

Hydropower projects based in south India account for 30% or 11,400MW of thecountrys installed capacity of 38,000MW of such power.Countrys total installed capacity of 147,000MW, only around 85,000MW isoperational at any given point of time.

India plans to add 78,577MW by 2012,

Indias track record in adding power generating capacity ,in the five years to2007, the country added 20,950MW of capacity, against a target of 41,110MW

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Electricity in India


India's peak power deficit is expected to widen in the current fiscal year to 12.6percent from 11.9 percent in the 2008/09 fiscal year that ended in March

Per capita electricity consumption rose from merely 15.6 kWh (kilowatt-hours) in1950 to.

In 2007-08 per capita consumption of power in India was about 717 kilowatt everyhour.

However, it is a matter of concern that per capita consumption of electricity isamong the lowest in the world.

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Electricity generation in India


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Demand of Electricity in India


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Electricity generation in India


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Transmission capacity in India


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Power stations in India


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Coal in India


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Coal


India ranks third amongst the coal producing countries in the world.

It accounts for 55% of the countrys total energy supplies.

Production of coal increased from about 70 MT (million tonnes) in early 1970s to534 million tonnes in 2009/10

Most of the coal production in India comes from open pit mines contributing toover 81% of the total production while underground mining accounts for rest ofthe national output .

Despite this increase in production, the existing demand exceeds the supply.

India's coal consumption will reach 604.3 million tonnes in the fiscal year toMarch 2010, leaving a shortfall of 70 million tonnes

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Coal Mines in India


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Cost Comparison Of ElectricityProduced By Various Fuels/Sources


Hydro Coal Diesel/solar3-4 rs/unit 4-5 rs/unit 12/20 Rs/unit

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Basic Thermodynamics


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First law of thermodynamics


The first law of thermodynamics is the application of the conservation of energy

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Energy conservation


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Second law of thermodynamics


The second law of

thermodynamics assertsthat energy has qualityaswell as quantity, and actualprocesses occur in thedirection of decreasingquality of energy. For

example, a cup of hot coffeeleft on a table eventuallycools, but a cup of coolcoffee in the same roomnever gets hot by itself (Fig.1-3). The high-temperature

energy of the coffee isdegraded (transformed into aless useful form at a lowertemperature) once it istransferred to thesurrounding air.

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Carnot Cycle


The Carnot cycle when acting as a heat engine consists of the following steps:

Reversible isothermal expansion of the gas at the "hot" temperature, TH(isothermal heat addition).Isentropic (reversible adiabatic) expansion of the gas (isentropic workoutput). For this step (B to C on Figure 1, 2 to 3 in Figure 2) the piston andcylinder are assumed to be thermally insulated, thus they neither gain nor loseheat. The gas continues to expand, working on the surroundings. The gas

expansion causes it to cool to the "cold" temperature, TC.Reversible isothermal compression of the gas at the "cold" temperature,TC. (isothermal heat rejection) (C to D on Figure 1, 3 to 4 on Figure 2) Nowthe surroundings do work on the gas, causing quantity Q2 of heat to flow out ofthe gas to the low temperature reservoir.Isentropic compression of the gas (isentropic work input). (D to A on

Figure 1, 4 to 1 in Figure 2) Once again the piston and cylinder are assumed tobe thermally insulated. During this step, the surroundings do work on the gas,compressing it and causing the temperature to rise to TH. At this point the gasis in the same state as at the start of step 1.

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The total amount of thermal energy transferredbetween the hot reservoir and the system

total amount of thermal energy transferredbetween the system and the cold reservoirwill be

The efficiency is defined to be

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Rankine cycle


There are four processes in the Rankine cycle,

Process 1-2: The working fluid is pumped from low to high pressure,Process 2-3: The high pressure liquid enters a boiler where it is heated at constantpressure by an external heat source to become a dry saturated vapor. The inputenergy required can be easily calculated using mollier diagram or h-s chart orenthalpy-entropy chartProcess 3-4: The dry saturated vapor expands through a turbine, generating

power. This decreases the temperature and pressure of the vapor, and somecondensation may occur. The output in this process can be easily calculated usingthe Enthalpy-entropy chartProcess 4-1: The wet vapor then enters a condenser where it is condensed at aconstant pressure to become a saturated liquid.In an ideal Rankine cycle the pump and turbine would be isentropic, i.e., the pumpand turbine would generate no entropy and hence maximize the net work output.Processes 1-2 and 3-4 would be represented by vertical lines on the T-S diagramand more closely resemble that of the Carnot cycle. The Rankine cycle shown hereprevents the vapor ending up in the superheat region after the expansion in theturbine,which reduces the energy removed by the condensers.

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The Steam Engine


In 200 B.C., a Greek named Hero designed a simplemachine that used steam as a power source.

A cauldron of water, placed above an open fire, Andheated, the cauldron shell transferred the heat to thewater. When the water reached the boiling point of 212F(100C), it changed into steam.

The steam passed through two pipes into a hollowsphere, which was pivoted at both sides. As the steamescaped through two tubes attached to the sphere, eachbent at an angle, the sphere moved, rotating on its axis.

Hero, labeled the device aeolipile, meaning rotarysteam engine.

Even today, the basic idea has remained the same generate heat, transfer the heat to water, and produce

steam.

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History of electric generation

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During the first two decades of the twentieth century, there was an increase in steampressures and temperatures to 275 psi (1.9 MPa) and 560F (293C), with 146F (81C)superheat.

In 1921, the North Tess station of the Newcastle Electric Supply Company in northernEngland went into operation with steam at 450 psi (3.1 MPa) and a temperature of 650F(343C).

The steam was reheated to 500F (260C) and regenerative feed water heating was usedto attain a boiler feed water temperature of 300F (149C).

Previously, as power generating stations increased capacity, they increased the numberof boilers, but attempts were being made to increase the size of the boilers as well.

Soon the size requirement became such that existing furnace designs and methods of

burning coal, primarily stokers, were no longer adequate.

Pulverized coal was the answer in achieving higher volumetric combustion rates andincreased boiler capacity.

The first use of pulverized coal in furnaces of stationary steam boilers had been

demonstrated at the Oneida Street plant in Milwaukee,Wisconsin, in 1918.

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Coal


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What is coal


Coal is a fossil fuel. It is a combustible, sedimentary, organic rock,which is composed mainly of carbon,hydrogen and oxygen.

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Coal


Coal is a fossil fuel formed in ecosystems where plant remains were preserved by

water and mud from oxidization and biodegradation.

Coal is a readily combustible black or brownish-black rock. It is a sedimentary rock,

It is the largest single source of fuel for the generation of electricity world-wide, aswell as the largest world-wide source of carbon dioxide emissions.

Coal is extracted from the ground by coal mining, either underground mining oropen pit mining (surface mining).

Coal is primarily used as a solid fuel to produce electricity and heat throughcombustion.

World coal consumption is about 6.2 billion tons annually, of which about 75% isused for the production of electricity .

Th Ad t f U i C l t

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The Advantages of Using Coal toMake Electricity


Cost

One of the biggest advantages of electricity produced by burning coalis its low cost.

Even compared to other non-renewable resources such as naturalgas and oil, coal is an economical energy source.

Availability

Another major benefit of coal is its availability.

Coal deposits are present around the world, making it easy to mineregionally. This means less cost and energy used to transport it

Chemical Energy to Heat Energy

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Chemical Energy to Heat EnergyCoal To Steam


Coal from the coal wagons is unloaded in the coal handling plant.

This Coal is transported up to the raw coal bunkers with the help of beltconveyors.

Truck and overland conveyor transportation are used primarily fordelivery of coal to plants near the mines or coal mine-mouth plants

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Coal Handling


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Coal Handling Bottom Unloading


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Coal Unloading


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Wagon Tippler


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Wagon Tippler


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Sea Transportation


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Coal crushing


In general, the size of the coal received at power plants is typically(0.30 m) or higher. The size required for the pulverizers used with mostpulverized coal steam generators (0.03 m). This requires the coal to bereduced by crushing before it is transported to the unit silos.

The ring granulator crusher is normally selected for power plantapplication, since its maximum product size can be controlled whileminimizing the amount of fines and dust produced.

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Coal Crusher


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Coal Handling Layout


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Steam Generators

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Coal To Electricity


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Chemical To Heat Energy-Boilers


The function of a steam generator is to provide controlledrelease of heat in the fuel and efficient transfer of heat to thefeed water and steam. The transfer of heat produces mainsteam at the pressure and temperature required by the

pressure turbine.

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Chemical To Heat Energy


Coal from the coal wagons is unloaded in the coal handling plant. Unloaded Coal is

crushed and transported upto the raw coal bunkers with the help of belt conveyors.

Coal is fed to Bowl Mills by Coal feeders. Coal is pulverized in Mill, to a powder form.

This crushed coal is taken to the furnace with the help of hot and cold air mixturefrom P.A. Fan. Atmospheric air from F.D. Fan is heated in the air heaters and sent to

the furnace as combustion air.

Water from the boiler feed pump passes through economiser and reaches the boilerdrum. From drum it passes through down-comers and goes to bottom ring header.Bottom ring header is divided to all the four sides of the furnace.

Density difference drives the water up in the water wall tubes "Water is partlyconverted to steam as it rises up in the furnace. From the water mixture , steam isseparated in drum.

Water follows the same path while the steam is sent to superheaters forsuperheating. The superheaters are located inside the furnace and the steam is

superheated ( 540"C) and finally it goes to turbine.

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Coal To Electricity Contd


These flue gases emits their heat energy to various superheaters in the panthouse and finally passes through air preheaters and then goes to electrostaticprecipitator where the ash particles are extracted.

Electrostatic precipitator consists of metal plates which are electrically charged.Ash particles are attracted on to these plates, so that they do not pass through

the chimney to pollute the atmosphere.

Regular mechanical hammers blows cause the accumulation of ash to fall tothe bottom of the precipitator where they are collected in a hopper for disposal.This ash is mixed with water to form a slurry and is pumped to ash pond.

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Early Boiler Designs 1920-1933


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Modern Boiler


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Combustion


Combustion can be defined as the rapid chemical reaction of oxygenwith the combustible elements of a fuel.

Chemical union of the fuel combustibles and the oxygen of the air, ata controlled rate produces useful heat energy.

Coal is a hydro carbon comprising of CHNOS as its elementalconstituents

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Combustion Heat Release


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Coal Combustion

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Various Equipments involved in coal combustion are:

Furnace; Drum; Boiler circulating pumps; Convection pass Superheater, Reheater,

Economizer; Air heater; Air preheat coils; Soot blowers; Coal feeders; Pulverizers;

Coal piping; Burners; Igniters and warmup burners; Ductwork; and Insulation.

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Basic Rankine Cycle Recap


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Superheating


The amount of work done in a turbine

depends is limited by the moisture contentin the steam.

A super heated steam improves cycleefficiency and reduces the moisturecontent in the steam.

The super heater heat transfer surfacemay be radiant surface in the furnace orconvective surface in the convection pass.

Tube materials typically are selected bythe boiler manufacturer based on thetemperature of the tube surface duringoperating conditions.

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Rankine Reheat Cycle


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FD Fan


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Coal Mill


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Economizer


Economizers are heat exchange devices that heat water, up to but notnormally beyond the boiling point of that fluid.

Economizers make use of the enthalpy in flue gas that are hot, but nothot enough to be used in a boiler, thereby recovering more useful enthalpyand improving the boiler's efficiency.

They are fitted to a boiler which saves energy by using the exhaustgases from the boiler to preheat the cold water used to fill it.

The economizer is composed of low-temperature convection passsurface.

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Boiler Auxiliaries Air Preheater


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Air pre heaters


The purpose of the air pre heater is to recover the heat from the boiler flue

gas. It increases the thermal efficiency of the boiler by reducing the useful heatlost in the flue gas.Two types Tubular and Plate type

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Electrostatic precipitator


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Steam To Mechanical Power


Steam from the control valves enters the high pressure cylinder of the turbine, where itpasses through a ring of stationary blades fixed to the cylinder wall. These act as nozzles

and direct the steam into a second ring of moving blades mounted on a disc secured to theturbine shaft. This second ring turns the shafts as a result of the force of the steam. Thestationary and moving blades together constitute a 'stage' of the turbine and in practice manystages are necessary, so that the cylinder contains a number of rings of stationary bladeswith rings of moving blades arranged between them. The steam passes through each stagein turn until it reaches the end of the high pressure cylinder and in its passage some of its

heat energy is changed into mechanical energy.

The steam leaving the high pressure cylinder goes back to the boiler for reheating andreturns by a further pipe to the intermediate pressure cylinder. Here it passes throughanother series of stationary and moving blades.

Finally, the steam is taken to the low pressure cylinders, each of which it enters at the

centre flowing outwards in opposite directions through the rows of turbine blades -anarrangement known as double flow - to the extremities of the cylinder.

As the steam gives up its heat energy to drive the turbine, its temperature and pressure falland it expands. Because of this expansion the blades are much larger and longer towardsthe low pressure ends of the turbine.

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Types Of Turbine


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Turbine


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Turbine


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Condenser


When as much energy as possible has been extracted from the steam it is

exhausted directly to the condenser.

The condenser consists of a large vessel containing some 20,000 tubes, eachabout 25mm in diameter.

Cold water from the river, estuary, sea or cooling tower is circulated through

these tubes and as the steam from the turbine passes round them it is rapidlycondensed into water condensate. Because water has a much smallercomparative volume than steam, a vacuum is created in the condenser.

This allows the steam to reduce down to pressure below that of the normalatmosphere and more energy can be utilized.

From the condenser, the condensate is pumped through low pressure heatersby the extraction pump, after which its pressure is raised to boiler pressure bythe boiler feed pump.It is passed through further feed heaters to the economiserand the boiler for reconversion into steam.

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Condenser


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Heat Balance Diagram


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Feed Water Heaters


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De-aerator


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Generator


The rotational mechanical energy is converted to electrical energy in the

generator by the rotation of the rotor's magnetic field. The rotation of the turbineturns the rotor of the generator, producing electrical energy in the stator of thegenerator.

The generator rotor consists of a steel forging with slots for conductors that arecalled the field windings. An electrical direct current is passed through the

windings, causing a magnetic field to be formed in the rotor. as this magneticfield is rotated by the turbine. The rotor is surrounded by the generator statorthat includes copper conductors. The magnetic field of the rotor passes throughthe stator, setting electrons in the stator conductor in motion.

The flow of electrons is called current. As the rotor's north pole passes through

the stator conductors, the current flows in one direction. When the south pole ofthe rotor's magnetic field passes through the same conductor, the current flowsin the opposite direction. This type of electrical current is called alternatingcurrent (ac) and is the type of current produced in most power plants.

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Switching and Transmission


Electricity is usually produced in the stator windings of large modemgenerators at about 25,000 volts and is fed through terminal connectionsto one side of a generator transformer (1) that steps up the voltage to132000,220000 or 400000 volts.

From here conductors carry it to a series of three switches comprisingan isolator (2), a circuit-breaker (3) and another isolator (4).

From the circuit-breaker the current is taken to the busbars (5)-conductors which run the length of the switching compound - and then to

another circuit-breaker (6) with its associated isolators (7), before beingfed to the Grid (8). Each generator in a power station has its owntransformer, circuit-breaker and associated isolators but the electricitygenerated is fed into a common set of busbars.

S

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Switching and Transmission


Th k Y

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Thank You

CoalToElec 18.10.2010

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