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    Coal and Ash Handling Coal and Ash Handling Presentation Transcript

    • COAL AND ASH HANDLING --VANITA THAKKARVANITA THAKKAR ASSOCIATEASSOCIATE PROFESSORPROFESSOR MECHANICAL ENGINEERING DEPARTMENT,MECHANICAL ENGINEERING DEPARTMENT, BABARIA INSTITUTEBABARIA INSTITUTE OFOF TECHNOLOGY, VARNAMA,TECHNOLOGY, VARNAMA, VADODARA.VADODARA.
    • Coal is the main fuel used in Thermal Power Plants across India. TYPES OF COAL:  Peat  Lignite  Semi bituminous  Bituminous  Anthracite INTRODUCTION 2VANITA THAKKAR BIT, VARNAMA
    • COAL ANALYSIS Ultimate Analysis : to determine the constituent of coal, but rather in a form of its basic chemical elements. Constituents % Moisture 3-30 Volatile Matter 3-50 Ash 2-30 Fixed Carbon 16-92 Constituents % Carbon 50-95 Hydrogen 1-5.5 Oxygen 2-40 Sulpher 0.5-3 Nitrogen 0.5-7 Ash 2-30 Proximate Analysis : to determine the amount of fixed carbon (FC), volatile matters (VM), moisture, and ash within the coal sample. 3VANITA THAKKAR BIT, VARNAMA
    • RECALL : GCV : Gross calorific value : The amount of heat released during the combustion of a specified amount of fuel, determined by bringing all the products of combustion back to the original pre-combustion temperature, and in particular condensing any vapor produced. NCV : Net calorific value : The amount of heat released during the combustion of a specified amount of fuel, determined by subtracting the heat of vaporization of the water vapor from the higher heating value (GCV). Volatile Matter: Volatile matter present in coal may be combustible gases like CH4, H2, CO and other hydrocarbon or incombustible gases like CO2, N2 etc. Presence of incombustible gases is always undesirable because it reduces the GCV of the coal. 4VANITA THAKKAR BIT, VARNAMA
    • SOME IMPORTANT DEFINITIONS Clinker : When Temperature developed in coal burning is higher than the fusion temperature of ash, the ash melts. The melting ash engulfs the unburnt coal particles and forms a solidified mass which is known as clinker. It is formed while burning coal containing ash which has low fusion temperature. Weathering of coal: All coals tend to combine with oxygen and slow oxidation takes place. This process of oxidation without burning is called weathering of coal. Primary Air: The amount of air which is used to carry the coal and to dry it before entering into the combustion chamber is known as ‘Primary Air’ Secondary Air: The amount of air which is supplied separately for completing the combustion is known as ‘Secondary Air’. 5VANITA THAKKAR BIT, VARNAMA
    • OUT-PLANT HANDLING OF COAL Out plant handling means transfer of coal from mine or port to storage of coal at plant site (dead storage). 1. Transportation by Rail: 4000 TO 13000 TONS PER TRIP. 2. Transportation by Ropeways 3. Transportation by Transportation by Sea or River 4. Road 5. Transportation of coal by Pipeline 6VANITA THAKKAR BIT, VARNAMA
    • TRANSPORTATION OF COAL BY PIPELINES 7VANITA THAKKAR BIT, VARNAMA
    • UNLOADING OF COAL AT SITE  Unloading from ship :  Unloading equipment.  Self unloading ship.  Unloading from Rail car.  Unloading from truck (lifting trucks). 8VANITA THAKKAR BIT, VARNAMA
    • Rail car unloading featuring bottom dump by unloading bridge : 9VANITA THAKKAR BIT, VARNAMA
    • Rail car Unloading by rotary dump : 10VANITA THAKKAR BIT, VARNAMA
    • COAL STORAGE Storage of coal is undesirable, because it costs more as there is  risk of spontaneous combustion,  weathering,  possibility of loss and deterioration during storage,  interest on capital cost of coal lying dormant,  cost of protecting the stored coal from deterioration and so on. 11VANITA THAKKAR BIT, VARNAMA
    • TYPES OF COAL STORAGE  Dead Storage :  Supplies the coal where there is a shortage of coal in plant due to failure of normal supply of coal.  This is long term storage and 10% of annual consumption, so it requires protection against weathering and spontaneous combustion. 12VANITA THAKKAR BIT, VARNAMA
    • TYPES OF COAL STORAGE  Live storage :  Supplies coal to plant for day to day usage. Capacity of live storage is less then that of dead storage.  Usually stored in vertical cylindrical bunkers or coal bins or silo, from where coal is transferred to boiler grate.  Bunkers are normally diamond-shaped cross- section storage area, made up of steel or reinforced concrete. 13VANITA THAKKAR BIT, VARNAMA
    • PURPOSE OF DEAD STORAGE OF COAL  To prevent shutdown of power plant in case of failure of normal supplies of coal due to coal strike, failure of the transport system etc.  Storage permits choice of the date of purchase allowing management to take advantage of seasonal market conditions. 14VANITA THAKKAR BIT, VARNAMA
    • MEANS OF COAL STORAGE Storage in Coal Heaps : It is required to :  Keep coal at low temperature (>70ºC)  Prevention of air circulation from bottom of coal piles  Proper drainage of rainy water to prevent weathering – drainage should not be rapid to prevent washing away of coal. Hence, ground used for stocking should be dry and leveled for proper drainage and concrete-floored to prevent flow of air from bottom. Coal is piled at a height of about 10 to 12 m and compacted in layers of 15 to 30 cm. In dead storage, coal pile is sealed by asphalt, fine coal dust, bituminous coating or other coating material. 15VANITA THAKKAR BIT, VARNAMA
    • MEANS OF COAL STORAGE (contd.) Underwater Storage : Possibility of slow oxidation and spontaneous combustion can be completely eliminated by storing coal under water. 16VANITA THAKKAR BIT, VARNAMA
    • COAL STORAGE AT SITE : DEAD STORAGE 17VANITA THAKKAR BIT, VARNAMA
    • SITE SELECTION FOR COAL DEAD STORAGE POINTS TO REMEMBER : 1. The storage area should be free from standing water. 2. If well drainage is not available artificial drainage should be provided. 3. It should be free from all foreign materials like wood, paper rags, waste oil or material having low ignition temperature. 4. Handling cost should be minimum. 5. Pile should build up in successive layer and compact. 6. Pile should dressed to prevent entry of rainy water. 7. Alternative drying and wetting should avoided. 18VANITA THAKKAR BIT, VARNAMA
    • SITE SELECTION FOR COAL DEAD STORAGE (contd.) 8. Stoker size coal should be oil treated to prevent absorption of water, O2, and compaction which is not needed. 9. Side of pile should not be steep. 10. Air may circulate freely through pile for proper ventilation to keep temperatures low. 11. Hot surfaces or boiler blow down or hot water or steam pipes and tanks should far from coal storage. 12. Hot bright days are to be avoided. 13. There should be provision for temperature measurement at different points. 14. Conical piling should be avoided. 15. Fire fighting equipment should be easily available. 19VANITA THAKKAR BIT, VARNAMA
    • INPLANT COAL HANDLING Coal Delivery Road Rail & Ship Unloading Preparation Transfer Inplant Handling Weighting Furnace Fire Car shakers, Rotary car dampers, unloading bridges, Self unloading ship, lifts trucks cranes and buckets. Crushers, Sizers, driers Belt conveyers, Screw conveyers, Bucket elevator, skip hoist, flight conveyers. Bulldozers, scrapers, tramways, cranes and conveyers. Bins, bunkers, indicators, gates, and valves. Scales, coal meters and samplers. Covered storage Outdoor Storage InPlantHandling Transfer coal from coal storage at plant site to point of utilization. 20VANITA THAKKAR BIT, VARNAMA
    • DESIGN OF INPLANT COAL HANDLING SYSTEM POINTS TO REMEMBER : 1. Simple and sound, requiring minimum operations and transportation. 2. No double handling of coal in plant. 3. Handling unit should be centralized to facilitate inspection and maintenance. 4. Electric motors can be used as driver of mechanism. 5. Working parts should be enclosed to avoid abrasion and corrosion. 6. System should be able to supply required quantity of coal as per demand. 21VANITA THAKKAR BIT, VARNAMA
    • Inplant handling of Coal 22VANITA THAKKAR BIT, VARNAMA
    • 23VANITA THAKKAR BIT, VARNAMA
    • COAL PREPARATION PLANT 24VANITA THAKKAR BIT, VARNAMA
    • CRUSHING OF COAL Coal is crushed in two stages. In the first stage the 300mm size is reduced to 100 to 75mm and in the second stage from 75 to 100mm to below 6mm. In figure double roller crusher, single roller crusher and rotary breaker is shown. 25VANITA THAKKAR BIT, VARNAMA
    • VIBRATING SEPARATOR Sizer or vibrating separator is fitted after crusher to screen the coal crushed below set size. Over size coal is returned to crusher for further proper crushing. Generally it separates out oversize coal of size > 6mm. 26VANITA THAKKAR BIT, VARNAMA
    • TRANSFER OF COAL Equipments used in coal transfer are:  Belt Conveyer  Flight Conveyer  Screw Conveyer  Bucket Elevator  Grab Bucket Elevator  Skip Hoists 27VANITA THAKKAR BIT, VARNAMA
    • BELT CONVEYORS A very suitable means of Transporting, it can transfer large quantity of coal over large distance economically – low initial cost, low power consumption. Main parts are: Belt (made of rubber, canvas or balata) End Drums or pulleys Idlers Return Idlers 28VANITA THAKKAR BIT, VARNAMA
    • BELT CONVEYORS (contd.) It uses inclination upto 20º Avg. speed : 60 to 100 m/min Capacity : 50 to 100 tones/hr Max distance it can transfer : 400m Advantage:  Economical, Low power consumption.  Large capacity  Rate of coal transfer rapidly change  Low maintenance cost. Disadvantage:  Not suitable for shorter distance and inclination >20º  Not suitable for dust particles and slurry. 29VANITA THAKKAR BIT, VARNAMA
    • FLIGHT CONVEYER (SCRAPER)  It is used when coal is discharged at different points in bins situated below the conveyer.  All parts are made of steel and iron, so it can handle hot material.  It is totally enclosed, so dust of coal can get transferred.  It can transfer coal at high inclination. 30VANITA THAKKAR BIT, VARNAMA
    • FLIGHT CONVEYER (SCRAPER) (contd.) Advantages:  It requires small head room  Speed and so material transfer rate can easily change.  It can handle hot materials also. Disadvantages:  High wear and tear, so short life.  High maintenance required.  Speed is limited up to 300 m/min due to abrasive action of material.  High power consumption per unit of material transfer. 31VANITA THAKKAR BIT, VARNAMA
    • SCREW CONVEYOR  It is used for shorter distance.  Totally enclosed from atmosphere.  Coal dust can also be transferred easily.  It is generally used in metering of coal.  Driving mechanism is attached at end of the shaft.  Diameter : 15 cm to 50 cm.  Speed : 70 to 120 rpm.  Capacity : 125 tones/hr (max.). 32VANITA THAKKAR BIT, VARNAMA
    • SCREW CONVEYOR (contd.) Advantage:  Cheap initial cost.  Simple and compact  Dust tight.  It can transfer coal at high inclination also.  Most suitable for short distance. Disadvantage:  High power consumption.  Length is limited up to 30 m  High maintenance due to high wear and tear. 33VANITA THAKKAR BIT, VARNAMA
    • Centrifugal Type Continuous Type Height: 30.5 m max. Inclination with Vertical: 30º Chain speed : Centrifugal: 75 m/min Continuous: 35 m/min Capacity: 60 tones/hr BUCKET ELEVATOR  It is used for vertical lifts.  Buckets are fixed on chain which moves on two wheels or sprockets.  Buckets are loaded at bottom and discharged at top.  Continuous Type Bucket capacity is more than that of Centrifugal type. 34VANITA THAKKAR BIT, VARNAMA
    • GRAB BUCKET ELEVATOR  It is used for lifting as well as transfer.  It can be used with crane or tower.  Initial cost is high but operation cost is less.  It is used when another arrangement is not possible.  Bucket capacity : 2 to 3 m3  Distance : 60 m  Capacity : 100 tones/hr. 35VANITA THAKKAR BIT, VARNAMA
    • COAL BURNING SYSTEM  FURNACE : Confined space where fuel is burnt. Provides supports and enclosure for burning equipment.  For solid fuels, like coal, coke, wood, etc. : STOKERS to convey the coal, GRATE to hold the fuel.  For pulverized coal and liquid fuels : BURNERS. 36VANITA THAKKAR BIT, VARNAMA
    • SOLID FUEL FIRING  HAND FIRING :  Simple method.  No capital investment.  Used for smaller plants.  Not a continuous firing process.  Only very small furnaces can be fired by this method.  Poor response to load fluctuations.  Controlling draught is difficult. 37VANITA THAKKAR BIT, VARNAMA
    • SOLID FUEL FIRING (contd.) : MECHANICAL FIRING / STOKER FIRING (Medium and large size plants.) ADVANTAGES :  High combustion efficiency.  No coal preparation.  Low grade coal can be used.  Reliable firing system.  Less labour requirement.  Less smoke produced.  Minimum danger of explosion. DISADVANTAGES :  High initial cost.  Complicated construction.  Coal loss in moving through grates.  High maintenance/repair cost due to high furnace temperatures.  Excessive wear of moving parts by abrasive action of coal.  Difficult : Sudden variations in steam demand. 38VANITA THAKKAR BIT, VARNAMA
    • TYPES OF STOKERS : based on way of feeding coal on grate OVERFEED STOKER :  Coal is fed from above, air from bottom.  Layers from above (after flame):  Fresh Coal Zone.  Drying Zone.  Distillation Zone – losing volatile content.  Combustion Zone – incandescent coke.  Ash Zone. UNDERFEED STOKER :  Coal and air are fed from bottom.  Layers from bottom :  Green Coal.  Ignition Zone (VM + CO + CO2 + N2 + H2).  Incandescent coke (CO2 + O2 + N2 + H2O).  Ash .  Flame. 39VANITA THAKKAR BIT, VARNAMA
    • SINGLE RETORT UNDERFEED STOKER • Smaller size / capicity. • Screw feeder on a mechanical ram forces the coal upward along the length. • Typical capacity : 1500 to 15000 kg/hr. Troughs for feeding coal Openings for air 40VANITA THAKKAR BIT, VARNAMA
    • MULTIPLE RETORT UNDERFEED STOKER Larger underfeed stokers. Multiple retorts – can be 12. Inclination – 25o-30o Typical Capacity : 10000 to 250000 kg/hr. Some over-fire air used for complete combustion. Tuyeres in between retorts for air. Some over-fire air used for complete combustion. Steam or air operated Water sprays used to cool ash. 41VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES OF MULTIPLE RETORT UNDERFEED STOKERS  High combustion efficiency.  High part-load efficiency.  Self-cleaning grate.  Smokeless operation at even very high loads.  High combustion rate.  Grate bars, tuyeres and retorts not subjected high temperatures due to continuous contact with fresh coal.  Substantial amount of coal remains on grate  boiler remains in service during temporary breakdown.  Different varieties of coals can be used. 42VANITA THAKKAR BIT, VARNAMA
    • DISADVANTAGES OF MULTIPLE RETORT UNDERFEED STOKERS  High initial cost.  Larger space requirements.  Clinker formation not eliminated.  High rate of wear and tear due to moving parts.  Low grade fuels with high ash contents cannot be burnt economically. 43VANITA THAKKAR BIT, VARNAMA
    • CHAIN GRATE OVERFEED STOKER 44VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES OF CHAIN GRATE OVERFEED STOKERS  Simple in construction.  Low maintenance cost.  Low initial cost.  Self-cleaning stoker.  Heat release rates can be controlled by controlling the speed of chains. 45VANITA THAKKAR BIT, VARNAMA
    • DISADVANTAGES OF CHAIN GRATE OVERFEED STOKERS  Always some loss of coal by fine particles carried with ashes.  Temperature of preheated air limited to 180oC.  Not suitable for high capacity boilers (200 tonnes/hr or more) as small amount of coal is carried in the grate.  Clinker problem – common. 46VANITA THAKKAR BIT, VARNAMA
    • TRAVELLING GRATE OVERFEED STOKER 47VANITA THAKKAR BIT, VARNAMA
    • SPREADER OVERFEED STOKER 48VANITA THAKKAR BIT, VARNAMA
    • <30 mm PULVERISED COAL HANDLING SYSTEM 49VANITA THAKKAR BIT, VARNAMA
    • UNIT SYSTEM 50VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES OF UNIT SYSTEM  It is simple in layout and cheaper than central system.  The coal transportation system is simple.  It allows direct control of combustion from the pulverize.  The maintenance charges are less as spares required are less.  In the replacement of stokers, the old conveyor system can be used without much alteration.  Coal which requires drying for satisfactory function of the central system is generally supplied without drying in the unit system.  It affords better control of fuel feed into the boiler furnace. 51VANITA THAKKAR BIT, VARNAMA
    • DISADVANTAGES OF UNIT SYSTEM  The mill operates at variable load as per the load on the power plant which results in poor performance of the pulverising mill (more power consumption per ton of coal at part load).  The total capacity of all mills must be higher than that for the central system with the load factors common in practice.  The degree of flexibility is less than of central system.  The fault in the preparation unit may put the entire steam generator out of use because no storage of pulverize coal.  Strict maintenance is desired as the operation of the plant directly depends upon the pulverizing mill.  There is excessive wear and tear of the primary fan blades as it handles air and coal particles. 52VANITA THAKKAR BIT, VARNAMA
    • CENTRALIZED SYSTEM 53VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES OF CENTRALIZED SYSTEM  Central system is flexible and changes can be made to accommodate quick changes in demand.  There is always a supply of fuel available in reserve in the boiler bunkers.  Since any mill can be used to supply to any boiler, the outage of parts of the mills or even a short outage of entire pulverizing plant will not cause a boiler plant outage.  Pulverizer mills always runs at its rated load irrespective of the load on the plant, therefore its power consumption per ton of coal crushed per hour is less and capacity of mill required less comparatively. 54VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES OF CENTRALIZED SYSTEM (contd.)  Pulverizer can be shutdown when sufficient reserve capacity has been achieved. During peak load, this reserve capacity can fulfill excess demand of coal.  Good control over fineness of coal.  There is greater degree of flexibility as the quantity of fuel and air can be separately controlled.  Burners can be operated independently of the operation of coal preparation.  Primary fan can handle only air so no problem of excessive wear of blades.  More flexibility of fitting of burners. 55VANITA THAKKAR BIT, VARNAMA
    • DISADVANTAGES OF CENTRALIZED SYSTEM  Higher initial cost and  Occupies a large space due bulky storage bin  High auxiliary power consumption. So power consumption/ton of coal is more then unit system  Possibility of fire hazard due to the storage of pulverized coal.  Complex coal transportation system.  Driers are essential. 56VANITA THAKKAR BIT, VARNAMA
    • DISADVANTAGES OF CENTRALIZED SYSTEM (contd.)  Operation and maintenance cost are higher then unit system. Note: bin system is not adopted in large capacity plants because of dangers from EXPLOSION of coal air mixture and tendency of stored pulverized fuel to cake. Also it required more maintenance, losses of coal through vent, high initial cost, high operating cost. So universally Unit System is adopted for large capacity power plants. 57VANITA THAKKAR BIT, VARNAMA
    • TYPICAL FLOW PROBLEMS IN BINS 58VANITA THAKKAR BIT, VARNAMA
    • 1.Ball mill 2.Ball and Race mill 3.Impact or hammer mill 4.Bowl mill 59VANITA THAKKAR BIT, VARNAMA
    • BALL MILL Sharp changes in the direction of the mixture throws out over-sized particles (returned to drum) 10 tons of coal per hour with 4% moisture requires 28 tones of steel balls. There is 20-25kWh energy consumption per ton of coal. 60VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES OF BALL MILL  Simple operation.  Low initial cost.  Grinding elements are not seriously affected by metal scrap and other foreign material in the coal.  Suitable for wide range of fuels, including anthracite and bituminous coal.  Low maintenance cost. 61VANITA THAKKAR BIT, VARNAMA
    • DISADVANTAGES OF BALL MILL  Large and heavy in construction.  Consumes more power than other mills.  Poor air circulation, so works less efficiently with wet coals.  High operating cost. 62VANITA THAKKAR BIT, VARNAMA
    • BALL AND RACE MILL Rotating. Hold down upper race to adjust force needed for crushing Very widely used. Principle of operation : Crushing and attrition. 63VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES / DISADVANTAGES OF BALL AND RACE MILL ADVANTAGES :  Low power consumption.  Lower weight.  Lower initial cost.  Lower operating cost.  Suitable for variable load conditions.  Can handle coals containing as much as 20% moisture. DISADVANTAGES :  Greater wear compared to other pulverizers.  Leakage of fine coal through the mill. 64VANITA THAKKAR BIT, VARNAMA
    • BOWL MILL 65VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES / DISADVANTAGES OF BOWL MILL ADVANTAGES :  Lower energy consumption (12-15kWh/t)  Less overall dimensions.  Classifier can be adjusted to alter degree of coal fineness while mill is on.  Leakage of coal from mill casing is practically nil as it operates at negative pressure.  Less noisy. DISADVANTAGES :  Sensitive to metallic objects that enter with coal.  Uneven wear of grinding parts presents repairing complexities. 66VANITA THAKKAR BIT, VARNAMA
    • IMPACT OR HAMMER MILL For brown coals, peat, oil shales, etc. 67VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES / DISADVANTAGES OF HAMMER / IMPACT MILL ADVANTAGES :  Simple construction.  Low capital cost.  Requires minimum floor area.  Operational speed is high.  Wet coal can be pulverized. DISADVANTAGES :  High power consumption when fine coal is require.  Limited capacity.  Metal scrap cannot be allowed to enter the mill. 68VANITA THAKKAR BIT, VARNAMA
    • PULVERISED COAL BURNERS REQUIREMENTS:  Proper mixing of coal and primary air.  Bring mixture of coal and primary air in contact with secondary air to create sufficient turbulence.  Controlling of flame shape and flame travel.  Adequate protection against overheating and excessive abrasive wear.  Ensure complete combustion. 69VANITA THAKKAR BIT, VARNAMA
    • PULVERISED COAL BURNERS FACTORS AFFECTING PERFORMANCE :  Characteristics of fuel used.  Particle size of pulverized coal.  Mixing of air and fuel.  Proportions of primary and secondary air.  Volatile matter content in coal.  Furnace design. 70VANITA THAKKAR BIT, VARNAMA
    • PULVERISED COAL BURNERS TYPES :  LONG FLAME / U-FLAME / STREAMLINED BURNER  SHORT FLAME / TURBULENT BURNER  TANGENTIAL BURNER  CYCLONE BURNER 71VANITA THAKKAR BIT, VARNAMA
    • LONG FLAME/U-FLAME BURNER  Primary, secondary and tertiary air required for combustion.  Hot secondary air is introduced at right angles to the flame for necessary mixing for better and rapid combustion.  Flame travels longer to allow it to get sufficient time for complete combustion.  Used for low volatile coal. 72VANITA THAKKAR BIT, VARNAMA
    • SHORT FLAME / TURBULENT BURNER  Fire horizontally or at some inclinations by adjustments.  High turbulence is created for pulverized coal and hot secondary air going to the burner  mixture burns as soon as it enters  combustion completed in a short distance.  Generally preferred for high volatile coals.  All modern power plants generally use it. 73VANITA THAKKAR BIT, VARNAMA
    • TANGENTIAL BURNER  High heat release rates.  Simple operation.  Almost complete combustion can be achieved.  Liquid, gaseous or pulverized fuels can be readily burnt either separately or in combination. ADVANTAGES :Four burners located in four corners of the furnace. Fires in such a way that four flames are tangential to an imaginary circle formed at the centre. 74VANITA THAKKAR BIT, VARNAMA
    • TANGENTIAL BURNER FRONT VIEW : TOP VIEW : 75VANITA THAKKAR BIT, VARNAMA
    • CYCLONE BURNER 76VANITA THAKKAR BIT, VARNAMA
    • CYCLONE BURNER  Water-cooled horizontal cylinder.  Located outside main boiler furnace.  Crushed coal is fed and fired with high rates of heat release.  Coal combustion is complete before the resulting hot gases enter the furnace.  High temperature – about 2000oC is developed.  The liquid slag formed is discharged off. 77VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES OF CYCLONE BURNER  Crushed coal is used. So, no pulverizing equipment.  Removes most of the ash, about 60% as molten slag. Hence, only 40% of the ash leaves with flue gases (in pulverized coal firing, 80% of ash goes with flue gases).  Reduces erosion and fowling of steam generator surface due to low ash content in flue gases.  Best results in low grade fuels like Indian Coal.  Can be operated with less excess air.  High furnace temperature obtained. 78VANITA THAKKAR BIT, VARNAMA
    • DISADVANTAGES OF CYCLONE BURNER  High F. D. Fan pressure required  high power consumption.  Formation of relatively more NOx, which pollutes air.  Not suitable for high Sulphur content coal. 79VANITA THAKKAR BIT, VARNAMA
    • OIL BURNERS  Functions :  Mixing oil and air in proper proportions.  Prepare fuel for combustion.  Generally used in small capacity boilers for industrial process heating.  It has to prepare air-oil mixture requiring minimum excess air for achieving maximum temperatures. 80VANITA THAKKAR BIT, VARNAMA
    • PRINCIPLE OF OIL FIRING 81VANITA THAKKAR BIT, VARNAMA
    • TYPES OF OIL BURNERS  VAPOURIZING BURNERS :  Oil is vapourized / gasified by heating within the burner.  Used in blow torches, gasoline stoves, etc.  Not used in boilers for steam generation.  ATOMIZING BURNERS :  Oil is atomized by nozzle(s) and vapourization occurs in combustion space.  Used in oil-fired furnaces and boiler furnaces. 82VANITA THAKKAR BIT, VARNAMA
    • STEAM OR HIGH PRESSURE AIR ATOMIZING BURNERS  VAPOURIZING BURNERS :  Oil is vapourized / gasified by heating within the burner.  Used in blow torches, gasoline stoves, etc.  Not used in boilers for steam generation.  ATOMIZING BURNERS :  Oil is atomized by nozzle(s) and vapourization occurs in combustion space.  Used in oil-fired furnaces and boiler furnaces. 83VANITA THAKKAR BIT, VARNAMA
    • TYPICAL OIL BURNER Preheated Oil (93oC- 120oC) delivered under pressure through a tube. Steam or air supplied by annular area between oil pipe and concentric outer tube. Oil is broken down into small droplets by using air or steam under pressure. 84VANITA THAKKAR BIT, VARNAMA
    • MECHANICAL BURNER  Oil is pressurized by :  Positive displacement pump.  Centrifugal dispersal of oil from a rotating wheel.  Spray nozzle is used for oil injection under high pressure of about 25 to 35 bar.  The oil leaves the nozzle in atomized state.  Rotating Wheel Burner : Oil leaves orifice as hollow cone of fine fuel particles due to centrifugal action.  Widely used due to less auxiliary consumption and less excess air required. 85VANITA THAKKAR BIT, VARNAMA
    • GUN-TYPE (MECHANICAL) OIL BURNER 86VANITA THAKKAR BIT, VARNAMA
    • ASH HANDLING 87VANITA THAKKAR BIT, VARNAMA
    • WHY ASH HANDLING ??!! 88VANITA THAKKAR BIT, VARNAMA
    • REQUIRMENTS OF AHP 89VANITA THAKKAR BIT, VARNAMA
    • Mechanical AHS : Hot ash coming from boiler falls on a belt conveyor through a water seal – gets cooled on quenching – and is carried continuously by conveyor to ash bunker or dumping site. 90VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES / DISADVANTAGES OF MECHANICAL AHS : ADVANTAGES :  Low power consumption.  Continuous ash removal. DISADVANTAGES :  Suitable for coal- fired, low capacity plants.  Maximum capacity : 5t/h.  Short life span : 5- 10 years only. 91VANITA THAKKAR BIT, VARNAMA
    • Low Velocity Hydraulic AHS : Ash from furnace grate falls into a low velocity water channel (3 to 5 m/s) and goes to ash sumps. There, ash and water are separated. Water is reused. Capacity : 50t/h Distance : 500m 92VANITA THAKKAR BIT, VARNAMA
    • High Velocity Hydraulic AHS : Hoppers below boiler are fitted with nozzles on top (to quench ash) & sides (to drive ash). Cooled ash goes to water channel below, settles & is removed. Water reused. Capacity : 120t/h Distance : 1km PCBs use it. 93VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES OF HYDRAULIC AHS :  High capacity, so more suitable for modern large capacity thermal power plants.  Clean and dust-free operation.  Ash can be disposed upto a distance of 1km from the TPP.  Can also handle molten ash.  No moving parts in contact with ash. Hence erosion problem is minimum. 94VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES OF HYDRAULIC AHS :  Abrasive ash forms corrosive acids in contact with water.  Water channel and pump must be made of special wear resisting material. 95VANITA THAKKAR BIT, VARNAMA
    • PNEUMATIC AHS :  High velocity air steam is directed to collect ash and dust from all discharge points.  All collected ash – crushed on the way by crushers, if clinkers are present – drops into air stream.  Cyclone separators separate ash from air.  Ash is collected in hoppers for further handling for disposal by trucks.  Clean air is discharged from top of secondary air separator into atmosphere through exhauster.  Typical Ash handling capacity : 5 to30 t/h 96VANITA THAKKAR BIT, VARNAMA
    • PNEUMATIC AHS : 97VANITA THAKKAR BIT, VARNAMA
    • PNEUMATIC AHS : 98VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES OF PNEUMATIC AHS :  Dust-free operation.  No re-handling problem.  Dry ash handling eliminates chances of ash freezing, picking or sticking to storage bins.  Flexibility in operation to suit various plant conditions.  Installation cost per ton of ash handled is less than that in other systems. 99VANITA THAKKAR BIT, VARNAMA
    • DISADVANTAGES OF PNEUMATIC AHS :  Noisy operation.  Wearing of crusher and pipe lines by abrasive ash inflicts high maintenance cost. 100VANITA THAKKAR BIT, VARNAMA
    • STEAM JET AHS :  High steam jet is passed through a pipe to carry off dust and ash particles, instead of air stream.  Ash is separated in cyclone separator and deposited into ash hopper for further disposal by trucks. 101VANITA THAKKAR BIT, VARNAMA
    • ADVANTAGES / DISADVANTAGES OF STEAM JET AHS : ADVANTAGES :  No auxiliary drive required.  Less capital cost.  Less space required.  Installed at inaccessible / awkward positions also.  Economical for ash disposal – 200m horizontal distance, 30m vertical distance. DISADVANTAGES :  Noisy operation.  Erosion in pipelines due to abrasive ash.  Capacity limited to 5t/h. 102VANITA THAKKAR BIT, VARNAMA
    • 103VANITA THAKKAR BIT, VARNAMA
    • DUST COLLECTORS – WHY ?  Flue gas exhaust contains fly ash.  Flue gas exhaust in pulverized coal fired boilers contains 80% of ash content of coal.  Fly ash is very fine – most of the particles can pass through a 300 mesh (40m) screen – particle size varies from 1m to 80m – basic difficulty in handling.104VANITA THAKKAR BIT, VARNAMA
    • DUST COLLECTORS – WHY ? (contd.)  Fly ash pollutes atmosphere – harms human, animal and plant health.  So, concentration of fly ash in flue gas must be brought down to below 0.5 g/m3, before discharging into atmosphere.  High ash content in Indian coals – about 25% - 50%.  A 200 MW plant using pulverized coal produces about 250T of fly ash per day. 105VANITA THAKKAR BIT, VARNAMA
    • BASIC REQUIREMENTS OF GOOD DUST COLLECTOR  Ability to remove very fine fly ash particles.  Low capital cost.  Low operating and maintenance costs.  Good wear resistance against erosion caused by abrasive fly ash.  Minimum floor space requirement.  High efficiency at all load conditions. 106VANITA THAKKAR BIT, VARNAMA
    • TYPES OF DUST COLLECTORS 1. MECHANICAL DUST COLLECTORS : 1. DRY TYPE 1. GRAVITATIONAL 2. CYCLONE 2. WET TYPE 1. SPRAY TYPE SCRUBBERS 2. PACKED BED SCRUBBERS 3. IMPINGEMENT TYPE SEPARATORS 2. ELECTROSTATIC PRECIPITATORS 107VANITA THAKKAR BIT, VARNAMA
    • GRAVITATIONAL SEPARATORS : Work on principle of gravity. Advantages : •Simple. •Low capital and maintenance costs. Disadvantages : •Cannot remove fine particles. •Bulky. •Large space requirement. 108VANITA THAKKAR BIT, VARNAMA
    • CYCLONE DUST COLLECTOR Commonly used for stoker as well as pulverized fuel firing. Efficiency range : 60% - 90%. 109VANITA THAKKAR BIT, VARNAMA
    • CYCLONE DUST COLLECTORS (CONTD.) Advantages : 1. High efficiency for large size particles. 2. Low maintenance cost. 3. Simple, cheap and easy operation. 4. Increase in efficiency with increasing load. Disadvantages : 1. Efficiency decreases with fineness of particles. 2. High power requirement for higher vortex velocity of flue gases. 3. Large space requirement. 4. High pressure loss. 110VANITA THAKKAR BIT, VARNAMA
    • WET TYPE MECHANICAL DUST COLLECTOR (WET SCRUBBER) Principle : Fly ash and sulphur present in outgoing flue gases is removed by water spraying – as shown in the fig. To minimize corrosion problems, tank is lined with lead, pipes are lined with rubber and spray nozzles are made of vitrified material. Advantage : High efficiency (about 90%). Disadvantage : Large water consumption & Corrosion. Tangential entry 111VANITA THAKKAR BIT, VARNAMA
    • WET TYPE MECHANICAL DUST COLLECTOR (WET SCRUBBER) (contd.) 112VANITA THAKKAR BIT, VARNAMA
    • WET TYPE MECHANICAL DUST COLLECTOR (WET SCRUBBER) (contd.) 113VANITA THAKKAR BIT, VARNAMA
    • ELECTROSTATIC PRECIPITATORS WORKING PRINCIPLE : 114VANITA THAKKAR BIT, VARNAMA
    • ELECTROSTATIC PRECIPITATORS WORKING PRINCIPLE (contd.): 115VANITA THAKKAR BIT, VARNAMA
    • ELECTROSTATIC PRECIPITATORS WORKING PRINCIPLE (contd.): 116VANITA THAKKAR BIT, VARNAMA
    • ELECTROSTATIC PRECIPITATORS SCHEMATIC DIAGRAM OF ESP : 117VANITA THAKKAR BIT, VARNAMA
    • THANKS !!THANKS !! -- VANITA THAKKARVANITA THAKKAR ASSOCIATEASSOCIATE PROFESSORPROFESSOR MECHANICALMECHANICAL ENGINEERING DEPARTMENT,ENGINEERING DEPARTMENT, BABARIABABARIA INSTITUTE OF TECHNOLOGY, VARNAMA,INSTITUTE OF TECHNOLOGY, VARNAMA, VADODARA.VADODARA. vanitaa.thakkar@gmail.comvanitaa.thakkar@gmail.com 118VANITA THAKKAR BIT, VARNAMA