Steam Power Plants-1

7/30/2019 Steam Power Plants-1

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Steam Power Plants-IBy


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Powerand Energy are buzz words in todays world.

Electricity is emerged as basic necessity with Food,Shelter and Clothing for human being.

Life without electricity has become highly unimaginable.

Electric locomotives, Heating, Cooling, Fans, Blowers,

Motors, Illumination are some applications that converts

electrical energy into useful work.

2CH KODANDA RAMA RAO Asst.ProfessorGITAM UNIVERSITY


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Progress of any nation is measured in terms of per capitaconsumption of electrical energy.(KWH consumed perperson per year)

India- 500 KWH /person per year

UK- 15 times that of India

US- 30 times that of India

Reasons of Popularity of electricity:- Clean environment for user

Higher efficiency

Better controllability Quick transfer of power from source to load

Energy conservation is simple



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Power Generation Scenario In India

Thermal Power --- 1,00,000MW

Hydro Power --- 65,000MW

Nuclear Power --- 10,000MW

Other sources --- 20,000MW

Total Installed Capacity--- 1,95,000MW



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Sources Of Electrical Power Generation

A.Conventional SourcesThermal (Coal)

Nuclear

Gas

WaterB.Non conventional Sources

Wind

Solar- PV

Biomass



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Disadvantages Of Conventional Sources

Fossil fuels shall be depleted, forcing us to

conserve them and find alternative resources.

Toxic, Hazardous gases, Residues pollute

environment.

Overall conversion efficiency is very poor.

Sources are located at remote places with

reference to load, increasing transmission cost.Maintenance cost is high.



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Block Diagram OfCoal Fired Thermal Plant



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Coal Based Thermal Power Plant

India has rich stock of coal as natural resource.

Chemical energy stored in coal is transformed toelectrical energy.

Coal powder is fired in boiler that converts water intosteam at high temp. and pressure.

This steam is injected over the blades of steam turbine(prime mover) in controlled way and hence, rotor of 3 PHa.c. generator rotates.



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Mechanical energy is converted into electrical energy at rated

voltage(10-30KV).

Used steam is cooled down to water using cooling towers and

condensers.

This preheated water is again injected in boiler tubes to

convert back to steam.

Flue gases are passed into atmosphere and fine particles of

ash are collected through ESP.

Ash(40% of coal weight) is collected and transported to AHP.



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Merits of Coal Thermal Plant

Coal is cheap and available in abundance at present.

It is a time tested process, so no experimentation isrequired.

Less space required as compared to Hydro based

station and less hazardous than Nuclear power plant.

Less initial cost as compared to other conventional

process of power generation.



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Demerits of Coal Thermal plant

Calorific value (Kcal/Kg) of Indian coal is very low andlarge ash content.

Huge volume of ash is produced daily and its disposal is

burning issue today.

Atmospheric pollution is very high.

Transportation of coal to plant and transmission ofgenerated power to load centre involves large expenses.



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Power plants circuits



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Thermal ( Steam ) Power plants mainly

consists of 4 circuitsCoal and ash Circuit

Coal produced in the mining site is transported topower plant site

Coal handling equipment for generation ofsteam

The combustion of coal produces ashwhich iscollected and removed to ash storage yard throughash handling equipments



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Air and gas circuit FD or ID fans are used for supply the air to

combustion chamber of the boiler through air-

preheater The air preheater is placed in the path of flue gases to

preheat the air

The flue gases produced by combustion of fuels in the

boiler furnaces after passing around boiler tubes andsuper heater tubes

Pass through a dust collector or precipitator wheremost of dust is removed before venting it of toatmosphere through chimney



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Feed water and steam circuit: Prime mover develops power by utilizing steam generated in

the boiler

Then condenser is used to condense the steam coming out ofprime mover

Apump is used to feed the condensate to the boiler

The condensate leaving the condenser is heated in feedheaters through extracted steam from lowest pressureextraction point of the turbine

The feed water may also be supplied from external source tocompensate anyloss ofsteam and water.

In the boiler shell and tubeswater circulation is setup due to

density difference of water between low and hightemperature sections

Asuper heater is used to super heat thewet steam fromboiler drum and is then supplied to prime movers



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Cooling water circuit In the condenser, quantity ofcooling water required

to condense the steam is large and is taken either

from lake, river or sea The coolingwater is taken from upper side of the river

and then passed through the condenser

The hot water is then discharged to lower side of the

river The system is known as open system

Wherewater is not available in abundantwater fromcondenser is cooled either in cooling pond or in

cooling tower the system is known as closed system



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Main Components of Thermal Power Plants

1. Boiler

2. Super heater

3. Economizer

4. Air preheater

5. Reheater

6. Steam turbine

7. Generator8. Condensers

9. Cooling towers

10. Pumps

11. Coal mills

12. FD and ID Fans

13. ASH Precipitators

14. Water treatment plant



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Fuels used in thermal power plantCombustion of fuel is accomplished by mixing with

air at elevated temperatures

Oxygen in the air chemically unites with Carbon,Hydrogen of fuels and produce heat

In thermal power plants normally steam is

produced from water by using combustion heat offuels (Except in Gas turbines)

Various fuels were used in thermal power plants

Fossil fuels ( Coal, Oil & Gas)

Industrial waste gases

Synthetic fuels or SYNFUELS



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Coal Coal is the principal energysource for India because of itslarge deposits and availability

Coal originated fromvegetable matter, which grew millions

of years ago Trees and plants falling into water decayed and later

produced peat bogs Huge geological upheavals buried these bogs under layers of

silt Subterranean heat, soil pressure and movement of earth's

crust distilled off some of the bog's moisture and hardenedit to form coal

Basically classification of coal is based on Physical andchemical composition Peat Lignite and brown coal Bituminous coal Anthracite



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Coal properties There are certain properties of coal, which are

important in power plant applications

They are sulphur content, heating value

ash softening temperature

swelling index

grind ability, weather ability,


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Moisture

All coal contains some % of moisture and it is generally varies

from 3 to 30 %

Volatile matterThe volatile matter resent in the coal may me as high as 50%

The volatile matter may be combustible gases

(methane,hydrogen,co) and non-combustible gases(CO2,N2)These gases decrease heating value of coal and increase the

volume of the furnace required

ASH-This is resent in two forms

1.)fixed ashwhich is formed after burning

2.) free ash- formed from clay and impurities(it can be removed by

washing screening21

CH KODANDA RAMA RAO Asst.ProfessorGITAM UNIVERSITY

Di d t f h


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Disadvantages of ashincrease cost of transporting, handling ,storing.

Decrease the heating value of coal.

Carbon:gives heating value to coal

sulphar:- adds little heating valueIt is responsible to corrosion


D i bl ti f l


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Desirable properties of coal

High calorific value

Small sulphur content ( les than 1%)

Good burning characteristics for complete combustion High grind-ability index

Highweather-ability

Grading of coal done on the basis

Heating value

Size

Ash content

Sulphur contentAsh softening temperature



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Peat Low grade coal

First stage coal formation Contains 90% moisture

Small amount ofvolatile matter

Not suitable for power plants Used in domestic purposes

Requires 1-2 months for drying in sunlight

Peat (20% water, Dried) has CV of 16 MJ / kg



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Lignite (Brown coal) Intermediate stage of coal development

High amount ofmoisture 30-40% Brown in color

High heating value and carbon compared to peat

Should be stored to avoid spontaneous combustion

Used in pulverized form

Can be air dried easily

Suitable for local use instead of transporting



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Bituminous coal Containing 46-86% of fixed carbon and 20-40% ofVM

Ash content may vary 6-12 % High percentage of volatile matter CVof32 MJ / Kg

Available in two forms CAKING and NON Caking

Sub-Bituminous is having less moisture, ash than ligniteand no CAKING power, used in briquette or pulverizedform

Semi-Bituminous coal high carbon and heating value,

contain less moisture, ash, sulphur, &VM, Has tendencyto break into pieces



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Anthracite Coals Contains more than 86% fixed carbon &VM around 8%

Ignites slowlyhas high CV of 36 MJ / Kg Low ash, zero CAKING power

Difficult to pulverizeAnthracite coal



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Liquid fuels

They are easyto handle, store and to burn They have nearlyconstant heating values They are primarily a mixture ofhydrocarbon compounds, which

may also contain nitrogen, oxygen and sulphur The bulk of the hydrocarbons belong to the paraffin series, like

methane (CH4), ethane (C2H6) propane (C3H8) and butane(C4H10) which are gaseous, and pentane (C5H12) hexane (C6H14)and octane (C8H18) which are liquid at STP

In addition, there can be isoparaffins, cycloparaffins and aromaticcompounds


Carbon: 83 87% Hydrogen: 11 16%


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Carbon: 83-87%, Hydrogen: 11-16%,

Oxygen + Nitrogen 0-7%, Sulphur 0-4%

There can also be some moisture and sediment

Crude oil distilled into a number of fractions gasoline,aviation fuel, kerosene, light diesel oil, heavy diesel oil,lubrication oil

The heavier fractions are used for boiler fuels and chemical

production The required physical properties of fuel oil are

specific gravity,

viscosity, pour point, flash point and heating value



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Gaseous fuels Transportation of natural gas is made through pipelines Natural gas is the cleanest of all fossil fuels It is free from ash and mixes well with air to undergo

complete combustion producing verylittle smoke It consists of a mixture of the mostvolatile paraffins-

methane to pentane It has high hydrogen content and produces a

considerable amount of water vapour when burned The heat of combustionvaries from 33.5 to 40 MJ/m3 Since the major constituent of all natural gases is

methane Liquid natural gas (LNG) is transported byspecial

tankers and stored in spherical pressurevessels to beused when needed, particularly during peak load.


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Other fuels Industrial Wastes & Byproducts

blast furnace gas, coke oven gas, and refinery gas sugarfactory refuse (bagasse); saw mill wood dust, rice husk

Synthetic fuels

Gaseous and liquid fuels from coal economically and

environment friendly mannerLiquid fuels using mixtures of fine coal in oil have been

known as colloidal fuel, coal-in-oil and more recently,coal-oil mixtures (COM)


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Coal handling



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Pulverised coal system

In this system coal is ground to a fine in a pulverised mill and

stored in bunkers from where it is fed into the combustion

chamber by means of steam of hot air .

The air is used to dry the coal an conveying it to the furnace is

called primary air .

The air blow separately to complete the combustion is calledas secondary air


Advantages of pulverised coal system


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Advantages of pulverised coal system

Rapid combustion with out use of large

quantity of excess air.

Higher boiler efficiency because of better

combustion.

Low grade coal can be used.

Ash removal is easy.

Fluctuation of loads can be easily used.

Disadvantagesinstallation cost is high.Risk of explosions are more

Special equipment is required for starting the system34

CH KODANDA RAMA RAO Asst.ProfessorGITAM UNIVERSITY


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1.Ring Type Coal Crusher

2.Hammer Mill Coal Crusher

3.Brad Ford Breaker


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Ring Type Coal Crusher



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Hammer Mill Coal Crusher



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OPERATION The coal is fed at the top

Is crushed by the action of rings that pivot off centreon a rotor or by swinging hammers attached to it

Adjustable screen bars determine the maximum size ofthe discharged coal



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Brad Ford Breaker



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Brad Ford Breaker Bradford breaker which is used for large capacity work

It consists of a large cylinder made up ofperforatedsteel plates to which lifting shelves are attached on the

inside The cylinder rotating slowly at about 20 rpm receives

coal at one end

The shelves lift the coal up and then the coal drops

down by gravity



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Belt conveyors

Best suitable for transporting large quantity over large

distance

It consists of end less belt running over a pair of end pulleys

and supported by series of rollers.

The inclination at which coal can be successfully elevated by

belt conveyor is about 200

Average speed of belt conveyer is 60-100 m/min

Load carrying capacity of the belt is 50-100 tones/hr


Advantages


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AdvantagesIt is most economical method of coal transporting in

medium and large capacity plants

Min repair and maintenance cost

power consumption is minimum

Disadvantagesnot suitable for greater heights and small distance


Scre con e ors


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Screw conveyorsIt consists of end less helicoids screw rotating inside a

housing .the movement of screw drives the coal fromend of the conveyor to other end where it is discharged

This is used for small capacities

Its length is limited to 30 mSeed 70 to 120 RPM

Max capacity-125 ton/hr

Low initial costSimple and compact

Adaptable to space available

Dust roof 43CH KODANDA RAMA RAO Asst.ProfessorGITAM UNIVERSITY


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Disadvantages

High power consumption

Excessive wear and tear

Short life compared to belt conveyor



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Bucket elevatorsUsed for moderate lift ,the coal can be conveyed at a speed of

16-40m/min

Less power is required

Coal can be discharged at elevated laces

Less floor area is required

Disadvantages

Its capacity is limited


Pulverized coal handling system


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Pulverized coal handling system



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Bowl Mill


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Bowl Mill


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Ball and Race mill



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PulverizationAdvantages Low excess air requirement Less fan power

Ability to use highly preheated air reducing exhaust losses Higher boiler efficiency Ability to bum a wide variety of coals Fast response to load changes Ease of burning alternately with, or in combination with gas and oil

Ability to release large amounts of heat enabling it to generate about2000 t/h of steam or more in one boiler Ability to use fly ash for making bricks etc. Less pressure losses and draught need.



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Disadvantages

1. Added investment in coal preparation unit

2. Added power needed for pulverizing coal3. Investment needed to remove fly ash before ill fan

4. Large volume of furnaces needed to permit desired heatrelease and to withstand high gas temperature



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1. Grate-fired furnaces

2. Chamber-type or flame furnaces


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Combustion Equipment For Burning Coal Fuel bed furnaces (coarse particles)

Pulverized coal furnaces (fine particles)

Cyclone furnaces (crushed particles) Fluidized bed furnaces (crushed small particles)



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Grate



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Chamber type


F l b d f ( i l )


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Fuel bed furnaces (coarse particles)

There are two ways of feeding coal on to the grate

1. Overfeeding

2. Underfeeding


Overfeeding


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Overfeeding



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Overfeeding Receives fresh coal from top surface has following

distinct zones

Fresh or green coal

Coal losing moisture (Drying zone)

Coking layer (loosing of VM) Distillation zone

Incandescent coke ( Fixed carbon is consumed)Combustion zone

Ash layer progressively cooled

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CH KODANDA RAMA RAO Asst.Professor

GITAM UNIVERSITY

Operations


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Operations

Primary air gets warmed up as it flows through the ash

layer

As it passes through the incandescent coke layer(1200 C)Carbon converted to Carbon dioxide releasing heat

continues till oxygen is consumed, iflayer is thick CO2 isconverted to CO reducing layer temperaturewater gasreaction also takes

The stream while passing through distillation zone VM

is added In distillation zone moisture is added

Know stream contains N,CO2,CO,H2,VM&moisture

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For combustion of this streamA hot ignition point ( In the range of 1000-1300oC

Done by providing a fire brick lined arch which stores upthe heat and remains at high temperature

Sufficient fresh air

Secondary air or over-fire air

Turbulence

Providing secondary air at right angles to up-flowing gasstream emerging out of fuel bed

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Results Carbon is in CO, CO2 both are color less

Carbon with hydrogen in VM which will be cracked toform free carbon at high temperature suspended in gas

stream

IfBurner is not designed properlyor operated properlyleads to unburnt carbon particles this appears as blacksmoke on chimney top

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Underfeeding

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Underfeeding In underfeeding coal is fed from below

Primary air passing through holes in tuyeresdiffuses through spaces in the raw green coal

picking up moisture In distillation zone to streamVM is added

In incandescent zoneVM breaks readily burnswith secondary air present above it where it is fedfrom top

VM burning is somewhat cooler need longer timeto ignite and burn

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Mechanical StokersOverfeeding1. Traveling grate stoker

2. Chain grate stoker

3. Spreader stoker4. Vibrating grate stoker

Underfeed stoker

1.Single retort2. Multiretort

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Traveling grate stoker


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Traveling grate stoker

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Traveling grate stoker Grate surface is made up of Cast Iron bars joinedtogether by links to form endless belt

Belt wound around two sprockets

A coal gate regulates the depth of fuel bed Simultaneous adjustment of Fuel bed thickness,

primary air flow controls the burning rate so that atthe end of its rear ash only remains

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Advantages & Disadvantages Simple and Initial cost is low

Reliable in service and maintenance is low

Gives high rate of heat release per volume of thefurnace

Limited coal can be carried on grate

Clinker problems are common

Ignition arches are required

There is always some loss in the form of particles

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Spreader stoker

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Spreader stoker Coal from hopper is fed byrotating feeder Feeder normally will have Blades fitted on the

drum

Fine particles burn in suspension Speed of the feeder varieswith the steam output of

boiler Grate is made up of CI bars, Links underneath the

grate are connected to a lever Fuels used may be Bituminous, lignite, wood

waste, baggase Coal size used in 6-36 cm

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Advantages and DisadvantagesA wide variety of fuels can be used Clinker formation is reduced

High temperature preheated air can be used

Quick response to load variation

Gives equal pressure drop and proper airdistribution

Operation cost is lowDifficult to operate variable sized coal particles

Fly ash and entrapped carbon particles

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Underfeed stokers

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Multiple retort

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ASH HANDLING SYSTEM Mechanical Handling System

Hydraulic Ash Handling System

Low pressure System

High pressure System

Pneumatic Ash Handling System

Steam Jet System

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ASH HANDLING FLOW DIAGRAM


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ASH HANDLING FLOW DIAGRAM

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Mechanical Handling System


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In this type belt conveyor is used


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Used for low capacity power plants

Ash is quenched (cooled)by allowing it to fall through

water seal over the belt conveyor

Quenched ash is then carried to a dumping site over the

belt

This is continuous handling system in which powerconsumption is low

It handles 3.5 tons of ash per hour with a speed of

0.3m/min 77CH KODANDA RAMA RAO Asst.Professor

GITAM UNIVERSITY



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y g y

Low pressure System

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in this system trough provided below the boiler


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in this system trough provided below the boiler

furnace and water is made to flow through it

The ash directly falls into trough and is carried by

the water to the sump

The water and ash are separated with the help of

screen in the sump.

The water is pumped back to the trough and usedagain while the ash is carried to the dumping site

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Hydraulic Ash Handling SystemL S t


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Low pressure System

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High pressure System

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In this the the hoppers below the boiler is fitted with

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water nozzles at the top and at the sides.

Ash is quenched by the top nozzle and side nozzlesprovide the drive force for the ash.

The water and ash are separated with the help of

screen in the sump.

The water is pumped back to the trough and used

again while the ash is carried to the dumping site

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Advantages of hydraulic system


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Advantages of hydraulic system

clean, dustless and totally enclosed

Carrying capacity is large.

Discharge ash at a considerable distance of over

600m.

Can also handles a stream of molten ash

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In this system ash from boiler is pulverised in the


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y p

crushers

fine ash is then passed into stream of high velocity

air

Cyclone separators are used to remove ash from airstream

Clean air is send to atmosphereAsh is send to dumping site

System can handle 5-30 tons of ash /hr 85


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Advantages

D t b li i t d th t i l h dl d i


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Dust can be eliminated as the material are handled in

a closed circuit

Flexible and can fit varying conditions.

It can carry ash through long distance

Disadvantages

Maintenance charges are high due to wear out of pipe

line.

More nois than other s stem. 86CH KODANDA RAMA RAO Asst.Professor

GITAM UNIVERSITY

Dust collection


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the exhaust gas leaving the boiler contain

particles of solid matter in suspension

smoke, dust(fly-ash),un -burnt coal(cinder)

The quantity of dust is more in pulverised

firing .

Less in stroker

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Types of dust collectors


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Types of dust collectors

Mechanical dust collectors1. Wet type collectors

2. Dry type collectors

Electrical precipitators(dust collectors

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Wet type dust collector


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Wettype dust collector

Water is sprayed to separate dust from flue

gas

Induced fan is used to carry gas through

chimney

Water is carried to a sludge pond

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Dry type dust collector


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y yp

Inertia separators

Cyclone separator is one of the common forms of inertia

separators

Gravitational separators

It works slowing down gas flow so that dust particles remainin a chamber for a long duration so as to settle at the bottom

It req ires a large chamber and not s itable in po er plants

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Steam Power Plants-1