COAL HANDLING PLANTOBJECTIVE:Coal Handling Plant is a plant which handles the coal from its receipt fromCoal mines to transporting it to Boiler and store in Bunkers. It also processesthe raw coal to make it suitable for Boiler operationA typical coal handling plant in any power plant shall have the followingprocesses in sequence depending on the capacity of the plant.1. Unloading process2. Feeding Process3. Screening Process4. Crushing Process5. Stacking Process6. Reclaiming Process7. Bunkering ProcessThese processes are explained in successive pages along with figures andflow diagrams. Other important accessories in coal handling plant like magnetic separators and suspended magnets are explained at the end.
Unloading processNormally thermal power station receives the coal by three modes ofoperation By Railway By Road By Arial ropewaysAerial ropeway is available only to the power stations which are nearthe coal mines.Cost of coal transportation by road is much higher than that for railTransport and hence most of the coal requirement of the powerstations is fulfilled by railway transport by Wagon Tipplers or byBOBR (Bottom Open Bottom Discharge) Wagons.
Wagon TipplersThese are the giant machines having gear boxes and motor assemblyand are used to unload the coal wagons into coal hoppers in very lesstime(e.g.20 wagons/hr. or more) For coal handling plant, wagon tippler arrangement is provided in most of the power plants where bottom discharge wagon are not feasible. Wagon tipplers are at present available to unload 20 tips per hour of 55 ton capacity wagons. A typical Wagon Tippler is shown in the next page.
Track HopperTrack Hoppers are mainly used for coal storage & handling in powerplants. The coal is generally transported from coal mines either by BOBRwagons (Bottom Open Bottom Discharge), or by Top open wagons & rarelyby trucks.A standard Track hopper is approximately 210m long. This length of trackhopper can accommodate at least 15 BOBR wagons. Each BOBR wagon cancarry approximately 45Mt of coal. Hence each length of track hopper,carrying 15 BOBR wagons can unload 675Mt of coal in approximately30minutes.An assembled Track Hopper is made from a large number of mechanicalitems. To name a few items are as listed below:(1) Reinforced cement concrete (RCC) hopper of 210m long and 8m wide(2) Steel Gratings covering the RCC hopper(3) Two parallel rail tracks running at the center of the hopper (210mlength).(4) Paddle/Plough Feeder located at the discharge side of the RCC hopper(5) Trough Conveyor located at the discharge of the paddle feeders.
RCC HopperThese hoppers function as a storage arrangement for discharged coal.Coal filled BOBR wagons are stationed above the 210m long RCChoppers.BOBR wagons are fitted with a bottom opening mechanism whichoperates on electrical power. The bottom doors automatically actuatesto discharge the coal into the hopper.The coal is transferred from wagons to RCC hopper under gravity. Forsafety reasons, galvanized steel gratings cover the entire top surface ofthe RCC hopper. These gratings are removable in times of need.Paddle/ Plough FeedersAfter the material is discharged from the wagons, they got stored in the RCChoppers. Paddle /Plough feeder is a mechanism used for the evacuation ofcoal from the bottom of RCC hoppers. As the name suggests, the feederploughs the accumulated coal from the bottom of the hopper and feeds itinto a moving belt conveyor. Its construction is like fan with few blades,mounted on a trolley.
Feeding ProcessThe feeding process involves continuous and control coal flow to meet therequirement.The efficient and economical storage, movement and control of large coalhandling installations, coal car unloading, storage & reclaim system dependon the proper application of feeders.FeedersVarious types of feeders are used for these processes. Feeders protect thebelt conveyors from damage by feeding the material onto the belt conveyorsfrom storage hoppers, at a controlled rate. These feeders are located belowhoppers for feeding of material at uniform rate to Belt Conveyors.The feeders, which are mainly used in the CHP, are listed below.1)Belt Feeder2)Apron Feeder3)Vibrating Feeder
Screening ProcessThere are three basic types of screening processes. 1)Scalping, 2)Fines removal 3)Grading.ScalpingFor scalping operations at the coarse end of particle distribution, very highscreening capacities can be achieved since most of the particles are muchsmaller than the screen opening and pass through quite easily. VibratingScreens and Roller Screens are generally used in CHP. But now days rollerscreen are used.Vibrating ScreensVibrating screens are of gravity feed type, being sloped downward from thefeed to discharge end. A high frequency low magnitude vibration is given tothe screen by an electric vibrator or other means. The purpose of vibration isto keep the meshes clear of wedged particles and stratify the coal so thatfine particles come down in contact with the screen.
Roller ScreenThe coal is feed on the rollers, which are continuously rotate. While rotatingthese shaft, transfers the coal from feeding end to crushing process end. Therequired size of coal is passed through gap of roller shafts. The remainingcoal is passed through rollers to crusherCrushing ProcessThere are four basic processes to reduce the size of material. 1)Impact 2)Attrition, 3)Shear 4)Compression.In CHP, crushing process is the combination of Impact and AttritionProcesses. Some process involves Compression crushing.
Typical Impact Crusher The bottom of the Reversible Impactor is open, allowing sized materials to pass through almost instantaneously. Liberal clearance between hammers and the breaker blocks eliminates attrition. Crushing is by impact only. In crushing, impact is the sharp, instantaneous impingement of one moving object against another. Both objects may be moving (a bat connecting with a ball), or one object may be motionless (a golf ball hit off a tee).Typical Attrition Crusher When a Non-Reversible Hammer mill is used for reduction, material is broken first by impact between hammers and material and then by shear and a scrubbing action (attrition) of material against screen bars.
Typical Shear Crusher Shear is a trimming or cleaving action that is usually combined with other methods: single-roll crushers, for example, use shear, impact and compression methods combined. Shear crushing is usually called for under these circumstances: When material is somewhat friable and has relatively low silica content. For primary crushing with a reduction ratio of 6 to 1.Typical Compression Crusher This crushes by compression without rubbing. Hinged overhead and on the centerline of the crushing zone, the swinging jaw meets the material firmly and squarely. There is no rubbing action to reduce capacity, to generate fines or to cause excessive wear of jaw plates.
Stacking & Reclaiming ProcessStacking:In this process coal from unloading area shall be stored/stacked in a yardfor future use. This shall be done by using belt conveyor with telescopicchute arrangement.Reclaiming:In this process the stacked coal shall be reclaimed for sending to boilerbunkers. Reclaiming shall be done by bulldozer and grizzly hopperarrangement.Both the process shall be combined and executed by Stacker Reclaimers.This equipment receives coal from a charge conveyor or discharge coalfrom a yard to a discharging conveyor. It is operated by complete remotecontrol with a computer.This shall be controlled by a PLC along with SCADA or by traditional joysticks.Typical stacker recalimer photos are shown below.
Bunkering ProcessThis process involves feeding of bins/bunkers and maintaining the level ofthese bins.From the conveyor belt the coal is discharged into bunker or bins with thehelp of trippers.The tripper is provided with wheels, which moves on rails parallel toconveyor on each side. It can be set in one position or made to travel slowlybackward or forward between stops; to discharge the quantity of coal atdesired location.Motorized trippers are usually used where continuous and uniformdistribution of coal along the conveyor is required or where frequent forwardor reverse movement is required.Trippers having rigid welded steel frame to resist shock and minimizedistortion. One way or two way discharge chutes are provided. Thebifurcating chute permits the flow and discharge of coal to the desired side.
Magnetic Separator and Suspended MagnetThere are more chances of ferrous metal pieces come along with coal frommines. It is essential to remove these metal pieces, to safe guard the crusherand belt conveyors from damage.Inline Magnetic Separators are provided, for continuous and automaticextraction and discharge of tramp magnetic pieces from coal beingdischarged from conveyors as specified.Suspended Magnetic Separator is provided for picking up tramp magneticpieces from moving coal over Conveyor.Mounting height of 400 mm shall be taken between top of conveyor belt orbottom of falling material trajectory and the surface of magnetic separatorbelt.The cross sections of magnet are suitably designed to provide sufficientarea for magnetizing the coil effectively, covering full cross section of thedischarge material.The magnetic separator is located such that it picks-up tramp iron from coaltrajectory, after it has been discharged from head pulley
Typical Coal Handling System FlowTo understand the coal flow staring from unloading area to coal bunker, letus take Arasmeta Captive Power Company Private Limited phase 2, CoalHandling System. The coal flow diagram is given in next page.Details of the flow diagram are explained.BCN – Belt Conveyor NumberBC – Belt ConveyorBCN1 is the belt which starts from the coal unloading area which lies inLafarge cement plant premises and has approximately 1000 M length.Coal from wagon tipplers are dropped in a chute at unloading area, and fromthere it will be dropped in BCN1 which is up to junction tower number 1From this junction tower, coal shall be taken by BCN2. This BCN2 hasmovable tripper, for stacking purpose in phase 1 side coal storage yard.Coal flow to bunker through various options are detailed in successive pages.
Sequence of coal flow from phase 1 secondary crusher to phase2 coal bunkerCoal from secondary crusher of phase1↓BC12↓BC13↓BC8↓BC9↓BC10↓BC11↓BC11AFor phase 2, coal from BCN2 shall be diverted by flap gate arrangement andcoal reaches BC2 through BC1. BC2 has movable tripper for stacking the coalin coal yard for phase 2.
The sequence of coal flow to phase 2 coal bunker from phase 2 coal yard.From reclaim hopper↓BC4↓Reversible belt feeder in Primary crusher↓If primary vibrating screen 1 is in line (OR) If PVS2 is in line↓ ↓BC5 BC6↓ ↓BC6 BC9↓ ↓BC9 BC10↓ ↓BC10 BC11↓ ↓BC11 BC11A↓BC11A
Coal flow from phase 1 secondary crusher and phase 2 coal yard to phase2 coalbunker is explained in the previous page.Similarly, from phase 2 secondary crusher, coal can be taken to phase 1 coal bunker.Refer the coal flow diagram, in junction tower 4 there is a flap gate through whichphase 2 coal shall be taken to phase 1 coal bunker through BCN8 which is present inphase 1 coal handling plant.