2. CONTENT
SL.No. TOPIC PAGE No.
1 2
Abstract
.
2 2
Introduction
3 2
Working of Coal Handling Plant
4 4
Availability of Coal in India
5 5
Transportation of Coal
6 5
CHP Auxiliary And Equipments
7 6
Operational Cycle.
8 7
Measures before Transporting Coal
9 7
Problems in coal handling plant
10 8
Dust management in thermal power plant
1
3. ABSTRACT
Many thermal power plants use coal as their fuel.To handle the coal, each power station is equipped with a coal
handling plant. The coal has to be sized, processed, and handled which should be done effectively and efficiently.
While working in the coal handling plant the major factor which reduces staff efficiency is the working environment
i.e., dust etc.. Generally all systems used in power station coal handling plants are wet dust suppression systems.
INTRODUCTION
Coal Handling Plant (CHP) is a plant which handles the coal from its receipt to transporting it to Boiler and store in
Bunkers. It also processes the raw coal to make it suitable for Boiler Opeartion.
Coal Handling Plant (CHP):-
Extent of work: - In brief we can say that receipt of coal from coal mines, weighing of coal, crushing it to required
size and transferring the quanta of coal to various coal mill bunkers. This is the responsibility and duty of the CHP and
its staff.
Receipt of Coal:-
Normally Thermal Power Station receives the coal by three modes of transportation.
1. By Railway (80-90% of the requirement is fulfilled by this way)
2. By Road ( if required 5-10% of the requirement is fulfilled by this way )
3. By Arial ropeways
General Working of a Coal Handling Plant :-
As mentioned above, coal is brought to power station by either of three means of coal transportation. This coal is first
conveyed to primary crusher with the help of different combination of conveyor belts and its rate of feeding is
controlled by Electro-magnetic vibrating feeders. Conveyor belt before the crusher is provided with hanging magnets
to separate ferrous materials. Stones are picked up manually. In primary crusher, coal is first crushed to 100 mm size.
This coal is again conveyed to secondary/final crusher on belt system. Here vibrating screens are used to feed
crushers, which bypasses coal of size more than 25 mm. In final crushers, coal is further crushed to required 25 mm
size. This sized coal is then send to bunkering belt and with the help of coal trippers. This sized coal is finally fed to
coal bunkers. This cycle is called coal bunkering.In case bunkers are full, then available coal is stored in stock yard
with the help of stacking belts /automatic stacker cum reclaimer. This cycle is called stacking.In emergency when coal
is not available in plant by railways/ropeways, then this stacked coal is diverted to the coal bunkers by reclaimimg
conv. belts. This cycle is called reclaiming. The coal stored in bunkers is further send to coal mill for pulverization
and combustion in boiler furnace.
2
4. GENARAL LAYOUT OF COAL HANDLING PLANT(CHP)
Availability of Coal In India :-
3
5. Mostly E and F grade coal used in India.
Blending Is Done To get Average D Grade.
e C.V. % Ash + Moisture
( K Cal / Kg. )
> 6200 19.57
5601-6200 19.57 - 23.97
4941-5600 23.92 - 28.69
4201-5940 28.69 - 34.05
3361-4200 34.06 - 40.14
2401-3360 40.14 - 47.10
TRANSPORTATION OF COAL:-
Coal is brought to the power station by three modes of transportation :
1.Roadways
2.Railways
3.Ropeways
1. Roadways :Coal is carried in trucks and a truck can carry about 8-10 tons of coal. But due to low capacity, low
unloading rate and time consuming, this mode is not in much use for large thermal power stations.
2. Railways :coal is brought by railway wagons. One rack consists of 58 wagons. Each wagon contains 58 MT of
coal. Locos bring the wagons from the marshalling yard and place them on wagon tippler. These wagons are then
4
6. unloaded with the help of wagon tippler. If these wagons are not unloaded in stipulated time period (generally 7 hrs.),
demurrage charges are lavied by railway department.
3. Ropeways :This mode of coal transportation is used where coal mines are located near the power stations. Coal is
brought by hanging buckets/trolleys travelling on track ropes, which are pulled by a haulage rope with a driving
mechanism. The payload of each bucket varies from 1 to 3 tons. Automatic loading and unloading mechanisms are
provided at loading and unloading stations. Rate of unloading varies from 75 to 275 MT/Hr depending on the type of
ropeways used. This type of coal transportation is very economical compared to road or rail transportation and gives
assured supply of coal, being the MSEB property. The only disadvantage of this system is long time for maintenance
works.
Coal HanndlingPlantAuxilaries:-
Major auxiliaries of CHP:-
1. Wagon Tipplers
2. Vibrating Feeders
3. Conveyor Belts
4. Coal Crushers
5. Trippers
6. Electromagnetic Separators
7. Dust extraction systems
8. Gas Extractor
Wagon Tipplers:-
These are the giant machines having gear boxes and motor assembly and are used to unload the coal wagons
into coal hoppers in very less time (e.g. 20 wagons/hr. or more).
Vibrating Feeders:-
These are electromagnetic vibrating feeders or sometimes in the form of dragging chains which are provided
below the coal hoppers. This equipment is used for controlled removal of coal from coal hoppers.
Conveyor Belts:-
These are the synthetic rubber belts which move on metallic rollers called idlers and are used for shifting of
coal from one place to other places.
Coal Crushers:-
We receive the coal in the form of odd shaped lumps. These lumps are to be crushed to required size. These
lumps are crushed by coal crushers.
Trippers:-
These are the motorized or manually operated machines and are used for feeding the coal to different coal
bunkers as per their requirement.
5
7. Electromagnetic Separators:-
Electromagnets are used for removing of Iron and magnetic impurities from the coal.
Dust Extraction System:-
This system is provided in CHP for suppression of coal dust in coal handling plant.
Gas Extractors:-
Gas extractors are provided at the bunker level to remove all types of poisonous and non poisonous gases
from the working area.
Operational Cycles:-
1. Normal Bunkering cycle.
2. Stacking cycle.
3. Reclaiming Cycle.
Normal Bunkering Cycle:-
Shifting of coal received from coal wagons directly to coal bunkers is normal bunkering cycle.
Stacking Cycle:-
When there is no coal requirement at coal bunkers even then CHP has to unload the received coal which is
stacked at open ground called yard. This is stacking cycle.
Reclaiming Cycle:-
when coal wagons are not available the requirement of coal bunkers is fulfilled from the stacked coal this is
reclaiming cycle.
Precautionary Measures before Transporting Coal
Weighing of Coal:-
Weighing of coal is carried out at wagon tippler. Weight of loaded wagon is taken; after unloading the coal,
weight of empty wagon is taken the difference of the two will give the weight of the coal (normally 55-60
metric ton of coal come in each wagon).
Payment of Coal:-
Payment of coal is made to the coalmines as per the weighing of coal carried out at their premises. However,
if any dispute arises regarding weighing of coal same is to be settled by the committee of both the parties.
Stone shells:-
Sometimes stone shells are received along with coal same has to be removed from the coal before bunkering
and is done sometimes manually or by different type of machines.
If quantum of stone shells is beyond minimum limit the cost of the coal is recovered from the coal mines
6
8. against the quantity of stone shells received from them.
Chemical Analysis of Coal:-
Sample of coal is randomly collected from each rake by concerned MSEB (Maharashtra State Electricity
Board) staff and detailed chemical analysis, calculation of calorific value is carried out and is confirmed
whether it is as per agreement with the coal mines or not.
General Problems faced in Coal Handling Plant :
1. DesignProblems :-Coal received in power station is having cal. Value much less and ash percentage more than
the rated values recommended by manufacturer. Hence the systems in coal handling plant get overloaded resulting in
low bunkering.
2. Rainy Season Problems :Chute choke ups, Coal yard -Slurry Formation Transfer chutes gets choked up due to
wet or muddy coal. Slurry formed in coal yard may cause problems with electro-magnetic feeders at input points,
frequent choke-ups at transfer chutes etc.
3. Other Misc. Problems: • Snapping of belts /ropes : Conv. belts and ropeway ropes get damaged or broken
because of jerks and overloading problems due to various reasons. Repairing and replacement of these belts and ropes
require more time for maint.
• Derailment of coal wagons :De-railment of wagons result in obstacle in unloading of balance wagons in line.
This results in lower bunkering and may attract demurrage charges from railway department.
• Oversized coal/Muddy Coal :Oversized / muddy coal may cause damage to the belt system, frequent choke-ups
of transfer chutes and damages to the crusher rings.
DUSTMANAGEMENTATCOALHANDLINGPLANTOFA THERMALPOWER
PLANT :-
INTRODUCTION :-
Coalfirethermal powerplantsare keysto power productionin thecountry.Theyplayvitalrolein power generationand
distribution, and constitute 64.75%oftotalpower productionin India. Sincecoal is thebasicrawmaterialusedinsuch
power plant,so they areequippedwithalargecoalhandling plant (CHP)wherecoaltransportedfrom coalminesare
storedandprocessedbeforesendingto boilerand steamgenerationsection.ACHPmayalsobecalled a"coalhandling
andpreparation plant"(CHPP).At this plant, major ergonomic concern is of dust particleswhich become
airbornewhile coalstorage andprocessing. CHPrequirevery largeareaforcoal storageandprocessing,
thereforelargescaledust generation occursatsuchplant.Peopleworkinghere becomevictimofPneumoconiosis whichisan
occupational lung diseaseandarestrictive lung diseasecausedby theinhalation ofdust. Thus ergonomic design
ofCHPisnecessary forbetterment ofworkersandauthority concern.SinceCHPrequire largeamount
ofwaterfordustsuppression, therefore innovative methodshave to be designin order to
minimizeuseofwater.Sincemany thermal power plant in India facing acute shortage of water, thereforeefficient
methodofdustsuppressionand prevention ishighlyrecommendedwhichusesleast amountofwater.Thefollowing
7
9. paperdiscusses design ofadustcollectorwhichdischarges dustin concentrated form in order to reduce water
consumption. ApartfromDustCollector, typical nozzledesign isalsoproposed which utilizes elegant
divergingwaterspray fordustpreventionminimizing waterwastage.Dustsuppression playsvitalrolein improving
performanceofworkers andtheirhealth, henceergonomic design ofCHPisveryimportant issue discussed at industry
level, especially at ThermalPowerPlant.
LayoutofaTypicalCoalFiredThermalPowerPlant
The abovediagram typically outline a coal fire thermal power plantwhere coaltransported fromcoal
minesthroughcoalvesselscalledwagonTripleris unloadedandcoalsiloisformed.Asclearlyoutline
themajorregionofdustgenerationwhileperforming above operations results in large scale airborne particles which must
be suppressed. We clearlydefinetheregionforwhichergonomicdesignshould
beproposed.Thedustparticlesemanatingfromcoal are typicallyis of size 1 to 100 microns. A typicalNTPC plant
requires 4.4 cubic meters per megawatt per hour.
DESIGNPROPOSALSFORDUST CONTROLATFIVEDIFFERENTSTAGESOF ATYPICAL
CHPOFA THERMALPOWER PLANT:-
Design proposalsfor preventing and suppressingdustatCHPusingefficientmethods.
Theabovefigureclearlydepictsthedesignproposal forpreventingandsuppressingdustat CHPusing efficient methods
8
10. and implementing cutting edge technology.Thegivendesignproposaltargetsfive
differentstageswheredustgenerationisquitelarge.
STAGE1
Atthisstage,coaltransportedfromcoal minesis broughtatCHPusingWagonTriplerandunloadedto
reclaimer.Largeamountofdustisgeneratedandin order toprevent dust, moisture addition is most
efficienttechniqueaswaterisverypowerfulbinding solvent. Directlyadding moistureto coal prevents dustfrom
becoming airborne.Herediverging nozzles areusedformoistureaddition.Divergingnozzlewill
allowoptimumproportionateofwatertobeadded withcoal.Sinceitisnecessarytoknow exactlywhat
amountofwatertobeaddedastoomuchwaterwill causemudandmakecoalheavier,ontheotherhand, toolittlewaterwillbe
ineffectiveindustcontrol.
STAGE2
Here(reclaimerstage)coalisunloadedfromwagon Triplertobereclaimed. Theareawherereclaiming is done is
quitelargeandhencewateraddition willbe futile.Alsowindplaydevastating roleinincreasing dust. Thuswind is themajor
factor.Sowindspeedi s c o n t r o l l e d inorderto preventdusttobecomeairborne.windshieldnetorwindbreakforest is
providedinordertoreduce dust generation.
STAGE3
Reclaimerpiles upthe coalatalargestorageareaand formsastackerorcoalpile.Whiledoing this,large amountof
dustisgenerated. Alsocoalstackerisa constantsourceofairbornedustparticles.Therefore itisnecessary tosuppress
dustgeneration.Atthis stagesurface compaction methodis usedtosuppress dust using 6-12% water solution of very
good binding substancewhichbindsthecoaldust and preventitfrom becomingairborne.Moisture addition
isdoneatthisstageusingwelldesigned spraywhich allowscontrolledflow ofsolution overcoalpilein ordertoproperly
suppressdustwithoutaffectingthe qualityofcoal.
STAGE4
Thisstageismajorareaofconcern becausedust particlesizeis aslow as1-10microns.Thereforethis stagerequires
asuitable,innovative andefficient technique of dust suppression. Since moisture addition
isfutileexercise,thereforewedevelopwet dustcollectorwhichcanreducedustconcentrationas
lowas1%intheconcernedarea.Dustcollectoris veryelegantdevicewhich discharges dustin
concentratedformreducingwaterconsumption.Even for suppressing1mm thick dust layer, we require largeamount
ofwater, but dust collectorwith minimumuseofwater,suppresses largeamountof dust. Thefollowing
sectiondiscussesdesign ofwet centrifugaldust collectorwithautomatic discharg for suppressingdustat this
stage.Hereprocessedcoal istransferredfromcoalstackthrough conveyorto
relaysection,hencelargeamountofdustisgenerated whichcanbe suppressedusingdustcollector.
STAGE5
9
11. Laststageisunloadingofcoalfromrelay section and transfer totheboilersection.Atthisstage,usual
methodofmoistureaddition issufficientsincesmall amount of dust generates which can easily be
suppressusingproperamountofmoistureaddition. Atthisstagealso,diverging nozzles ofoptimum diameterare used
forproperwater spray.
DESIGNOFAWETCENTRIFUGALDUST COLLECTOR :-
Centrifugal collectors usecyclonicactiontoseparate dustparticlesfrom thegasstream.Inatypical cyclone, the
dustgasstream enters atan angleandis spunrapidly.The centrifugalforce created bythe circular flowthrows the dust
particles toward the wall ofthecyclone. Afterstrikingthe wall,these particlesfallintoahopperlocatedunderneath.
Themostcommon typesofcentrifugal orinertial collectorsinusetodayare:
1) Single-cycloneseparators
2) CycloneMultiple-separators
3) SecondaryAir FlowSeparators
Atypicalwet centrifugaldustcollectorusesscrubbing effect ofwatertosuppressdust.Waterisverygoodbinding substance
fordust and therefore it is used as scrubbingelement.Thisdeviceappliestheprinciple
offilmformationoverthedustlayerandconfines dust particles leavingfreshairtoescape..Thepowerratingofmotorvaries
asperrequirement. This deviceuses theprinciple of dynamicprecipitation techniqueinwhichveryhigh suction pressure
suck the dusty air and allow to centrifuge through it. Centrifugal actionseparates dustfrom
freshairandfreshairisallowedtoescape fromotherendofdustcollector.
The dust collector has a small tank full of water whichhastwovalves. Thesetwosprings loaded
valvesareoperatedtoallow passageofconcentrated dust andautomatic filling of fresh water using
sensors.Thesesensorssensetheconcentrationlevel ofdustinthecontainerand whenit goesbeyond 90%,itopens
thedischargevalve.Thisremains open untiltotaldischarge ofconcentrated dust occurs from
thetank.Atthesametime,itopens inletvalveto allowfreshwaterto fillup.
The dust collector uses automatic discharge technique andhencesavetimeformanualoperations
fordischarging andrefilling.Alsodischargeis recycledin order to haveminimumwaterwastage. Thiscentrifugal
dustcollectorisvery efficientand requires minimum amount of water since it discharges dustin concentrated
form. Taking atypicalcaseof aNTPC plantwhichuses 4.4cubic meterpermegawattperhour,assuming power
productionof 1000MW, totalwaterconsumptionwill be4400 millioncubicmeterwater. Thisishuge amountofwaterwhich
10
