Electric power generation technologies p

Thermal ppt

1. COMPANY LOGO Electric Power Generation Technologies

2. Introduction Sources of Energy: Non-renewable sources: Fossil fuels like coal, natural gas, petroleum, Uranium and Plutonium Renewable sources: Sunlight, Wind, Water, Tides and waves, Geothermal heat, Biomass

3. Types of Power Plants: Thermal Hydro Nuclear Diesel Gas plants Renewable energy sourced plants

4. Electricity sector in India Installed capacity: 330.86GW Renewable Power Plants: 31.7% of total installed capacity Gross electricity generated by utilities in India was 1,236.39 TWh Total electricity generation (utilities and non utilities) in the country was 1,433.4 TWh or 1,122 KWh per capita India is the world's  third largest producer  and  fourth largest consumer  of electricity. Electric energy consumption in agriculture was recorded highest (17.89%) in 2015-16 among all countries. The per capita consumption is low compared to many countries despite cheaper electricity tariff in India.

5. Installed Capacity of various sources in India

6. Power crises in India Faulty planning Sharp increase in demand Delay in construction of power projects Inter-state disputes Erratic mansoon Plant outages Transmission losses Shortage of coal Poor utilisation of generating equipmemts

7. Thermal Power Plants Around 65% of India’s electricity generation capacity is from thermal power plants 85% plants are coal based 195,552.88 MW installed capacity Top 10 thermal power plants in India Vindhyachal Thermal Power Station, Madhya Pradesh Mundra thermal power station, Gujurat Mundra Ultra mega power plant, Gujurat Talcher Super Thermal Power Station, Odisha

8. Sipat Thermal Power Plant, Chhattisgarh NTPC Dadri, Uttar Pradesh NTPC Ramagundam, Andhra Pradesh Korba Super Thermal Power Plant, Chattisgarh Rihand Thermal Power Station, Uttar Pradesh Jharsuguda Thermal Power Plant, Odisha

9. Selection of site Nearness to the load centre Supply of water Availability of coal Land requirement Transportation facilities Labour supplies Ash disposal Distance from populated area

10. Thermal Power Plant Converts heat energy to electrical energy Coal is burnt in the boiler which converts water into steam Expansion of steam in turbine produces mechanical power which drives the alternator Sources of Energy: Coal Water Air

11. Coal Composition Carbon Moisture Ash Sulphur Nitrogen Hydrogen oxygen

12. Types of Coal The ash content in bituminous is 6-10% Semi-bituminous is widely used in power plants. Super-anthracite has little importance in power generation Type of coal Moisture content Carbon content Calorific value (kJ/kg) Peat 60-90% 5 -20% 3000 Lignite 30-50% 20-40% 13800-17600 Sub-bituminous 17-20% 60-80% 18800-23000 bituminous 17-20% 60-80% 23000-34000 Semi-bituminous 17-20% 60-80% 27000-35000 Semi-anthracite 5-10% 90% 33500-34750 anthracite 5-10% 90% 30000 Super-anthracite 5-10% 90%

13. Characteristics of coal Calorific Value Weatherability Sulphur content Grindability index Caking characteristics Ash content Particle size

14. Layout of thermal power plant

15. Schematic of a thermal power plant

16. Main and Auxiliary equipments Coal handling plant Pulverizing plant Draft fans Boiler Ash handling plant Turbine Condenser Cooling towers and ponds Feed water heater Economiser Superheater and Reheater Air preheater Alternator with exciter Protection and control equipments Instrumentation

17. Coal Handling Plant Automatic feeding of coal to the boiler furnace. 200MW plant may require around 2000 tons of coal daily. In every plant there is enough storage of coal to last for 15 days or so. Three Sections: Unloading Plant Conveying Plant Crushing Plant

18. Schematic diagram of CHP

19. Unloading Plant: The coal is brought to the power station site by rail wagons. The wagon tippler tilts the wagon and unload the coal into the hoppers. The coal from the hoppers is fed into the conveyer belts. Conveying Plant: The conveying plant consists of belt conveyors. The coal initially taken from hopper by the belt to the vibrating screens and then into the crushers. Coal from crusher falls either on bunkering belt or on stacking belt. On the various belts magnetic separators are provided to remove any magnetic iron materials such as bolts, iron scrap which may present in the coal so that it dost not go into the crusher and also into the bunkers at their final stage. Crushing Plant: Screens are provided to reduce the load on the crusher. The coal size of 19mm and below passes through it and remaining goes to the crusher. Coal of size larger than 19mm is crushed in the crusher.

20. Main Process Stacking Process: This process involves in dead storage in the form of piles laid directly in the ground. In case of road transport and aerial transport coal are unloaded in stack yard and the coal is stacked properly using dozers. When coal supply by railway is excess it would be stacked through a separate conveyor. For these purpose stacker or telescopic chutes are used. Reclaiming Process: The stored coal is required to bunkered in case of emergency or improper coal supply. The reclaiming process involves the lifting of coal from stack yard by means of dozer or reclaimer like bucket wheel. The dozer feed this coal in hopper. This process is simple process. The main object of this process to bunker crush coal or non-crush coal as per requirement of bunker to support the other process feeding. Bunkering Process: This process involves feeding of bins and maintaining the level of these bins. From the conveyor belt the coal is discharged into bunker or bins with the help of trippers. Capacity of bunker should be enough to feed coal to the boiler for at least 8 hr on full load. Coal stored in Yard, if rate of coal is faster than required.

21. Pulverizing Plant Coal is pulverized and carried to the furnace in the steam of hot air. Exposing a large surface of area to the action of oxygen and helping the combustion process. Advantages: Rate of combustion can be controlled Banking losses are reduced. Percentage of excess air requirement is low Preheated air can be used Wide variety of low grade oil can be used. Disadvantages: Investment cost of plant is high Explosion hazards exist Auxiliary power consumption of the plant increased Requires ESP to reduce stack emissions to acceptable limits. Extra equipment's, mills, burners are needed.

22. The pulverizer receives the raw coal and reduces it to a very fine, specified size consist similar to face powder. There are four principles involved in pulverization: Drying Grinding Circulation Classification

23. Drying: The coal that is passing through a pulverizer is entrained by the use of hot air usually from the air heater. During the pulverization process the surface area of the coal particles increases dramatically exposing fresh coal to the entrainment air. The inherent and surface moisture of the coal is reduced by the exposure of hot air. Grinding: There are three basic type of grinding: Impaction: where the material to be ground is hit or impacted by an outside force Crushing: where material is forced between two fixed object. Attrition: where material is ground by rubbing or friction

24. Circulation: The primary air, is the method of circulating the coal through the pulverizer. Circulating air is also important in allowing the removal of heavy material by centripetal force that otherwise might damage the grinding mechanism.

25. Classification: The circulating air is also used to classify the pulverized coal product prior to carrying it to the burner. The classifier, located on the top of a mill returns the over size material back to the pulverizer but allows the proper size material to pass out of the mill to the burners. Classifier are critical in providing in the desired quality of pulverized coal with the desired quality. Pulverized mills are: Contact Mill Ball Mill Impact Mill

26. a) Contact mill: A contact mill has stationary and power driven rotating elements, having a rolling action with respect to each other. Coal is made to pass between these elements again and again till it is pulverized to required fitness 2) Ball mill: A large cylinder partly filled with various sized steel balls, is used. The cylinder is rotated slowly while coal is fed into it. The balls pulverize the coal by crushing. 3) Impact mill: All the grinding elements and the primary air fan are mounted on a single shaft. The flow of air carries the coal to the primary stage where it is reduced to fine granular state by impact with a series of hammers. The coal is then carried by the flow of air to the final stage. Final stage consists of pegs carried on a rotating disc and completes the pulverizing process.

27. Draft or Draught System The combustion in the boiler requires supply of sufficient quality of air and removal of exhaust gases. The Circulation of air is caused by difference of pressure is known as draught. Thus draught is the differential in pressure between the two points. A draft may be Natural draft Mechanical draft. 1) Natural Draught A natural Draught is provided by the chimney or stack. Natural draught has its limitation. Modern plants has high rate of heat transfer and Draught losses are very high. In view of this Natural draught is used only for small boilers.

28. 2) Mechanical Draught Modern large size plants use very large size of boilers of capacity above 1000,000 kg per hour. Such boiler needs tremendous volume of air (around 200000 m 3 Per minute). A chimney alone cannot provide this. Therefore mechanical draught is used. In a mechanical draught the movement of air is due to the action of fan. A mechanical Draught consist of forced Draught or induced draught or both. In forced draught system the fan is installed near the boiler. The fan force the air through the furnace, economizer, air preheater and chimney. The pressure of air, throughout the system, is above atmospheric and air is forced to flow through the system In an induced draught system the , the fan is installed near the base of the chimney. The burnt gases are sucked out from the boiler, thus reducing the pressure inside the boiler to less than atmosphere. This induces fresh air to enter the furnace. A mechanical Draught need additional capital investment and maintenance. But it required for proper operation of modern power plant. In super thermal power plant, each boiler may used two forced fans and two induced fan.

29. Boiler A boiler (or steam generator) is a closed vessel in which water, under pressure , is converted into steam. The heat is transferred to the boiler by all three modes of heat transfer i.e. conduction, convection and radiation. Major types of boilers are: (i) fire tube boiler and (ii) water tube boiler

30. (i) Fire Tube Boiler: The boiler is named so because the production of combustion pass through the tubes which are surrounded by water. Depending on whether the tube is vertical or horizontal the fire tube boiler is divided into two types: Vertical tube boiler Horizontal tube boiler A fire tube boiler is simple, compact and rugged in construction. Its initial cost is low.

31. (ii) Water Tube Boiler: In this boiler, the water flows inside the tubes and hot gases flow outside the tube . Water tube boiler are classified as Vertical tube boiler Horizontal tube boiler Inclined tube boiler The circulation of water in the boiler may be natural or forced.

32. Forced circulation through the action of pump. Advantage of forced circulation: Lesser weight of boiler and cheaper foundation. Lighter tubes Greater freedom in configuration of furnace. Uniform heating of all parts. Increased efficiency of boiler Better control of temperature Quicker response to load change The factors which influence the choice of boilers are: Initial cost, availability, maintenance cost, labour costs, space and fuel cost

33. Super Heater & Reheater Superheater Super heated steam is that steam which contains more heat than the saturated steam at the same pressure. The additional heat provide more energy to the turbine hence power output is more. Superheated steam causes lesser erosion of the turbine blades and can be transmitted for longer distance with little heat loss The function of the super heater is to remove the last trash of moisture from the saturated steam. The heat of combustion gases from the furnace is used for superheating. A super heater may be convection type, radiant type or combination

34. Types of super heater Convection type: Placed somewhere in the gas stream and receives its heat entirely from flue gas through convection has rising characteristics i.e. temperature of superheat increases with increase in steam output These are commonly used superheaters.

35. Radiant type: Located in the furnace waterwalls and absorbs heat from the burning fuel through radiation Two disadvantages: Owing to high temp of furnace it may get over heated so design should be done carefully It gives drooping characteristic i.e. the temp of the superheat falls with increase in steam output , because with the increase in the steam output, the furnace temp rises at much less rapid rate than the steam output and the radiant heat transfer being a function of furnace temp increases slowly with steam flow or the steam temp falls Advantages of superheating: Reduction in requirement in steam quantity for a given output of energy Turbine size is reduced Due to dry steam the mechanical resistance to the flow of steam over the turbine is small resulting in high efficiency No corrosion and pitting at the turbine blades, so their age increases.

36. Re-heater:   Some of the heat of superheated steam is used to rotate the turbine where it loses some of its energy. Re-heater is also steam boiler component in which heat is added to this intermediate-pressure steam, which has given up some of its energy in expansion through the high-pressure turbine. The steam after reheating is used to rotate the second steam turbine where the heat is converted to mechanical energy. This mechanical energy is used to run the alternator, which is coupled to turbine, there by generating electrical energy.

37. Economiser Flue gases coming out of the boiler carry lot of heat. An economiser extracts a part of this heat from flue gases and uses it for heating feed water. This use of economiser results in saving coal consumption and higher boiler efficiency.

38. Air Preheaters After the flue gases leave economizer, some further heat can be extracted from them and is used to heat the incoming air for combustion. Air preheaters may be of following types: Plate type Tubular type Regenerative type Cooling of flue gases by 20 o increase the efficiency of the plant by 1%. Air Preheater (Regenerative)

39. 1) Plate Type: Plate type air heater has alternate narrow lanes for gas and air passages. The two fluids flow in opposite directions. 2) Tubular Type: In tubular air heater, the gases flow inside the tubes and the air over the tube exteriors. 3) Regenerative Type: A regenerative air heater uses a cylindrical rotor made of corrugated steel plates. The rotor is fixed on to a shaft which is rotated at 2-4 rpm. As rotor rotates, it passes through flue gases and air zones. The rotor elements are heated by the flue gases in their zone and transfer this heat to air when they are in the air zone.

40. Steam turbine A steam turbine converts heat energy of steam into mechanical energy and drives the generator. It uses the principle that steam when issuing from a small opening attains a high velocity. This velocity attained during expansion depends on the initial and final heat content of the steam. This difference b/w initial and final heat content represents the heat energy converted into kinetic energy. These are of two types :- Impulse turbine Reaction turbine

41. Turbine

42. Turbine – Full View

43. Impulse turbine: Steam is expanded in steam nozzle and attains a high velocity The steam jet impinges on the blades fixed to rotor periphery Two types of rotors: Built-up rotor: consists of a forged steel shaft and the blades are forged steel discs which are shrunk and keyed Integral rotor: the blades and shafts are formed from one solid forging. HPT and IPT are always forged type Complete expansion of steam takes place in the nozzle Pressure is same through out the turbine and on both side of the blades Blades have symmetrical profile

44. Reaction turbine: Only partial expansion takes place in the nozzle and further expansion takes place on the rotor blades Pressure difference on both side of the blade The relative velocity increases as it expands while passing over the blades Aerofoil sectioned blades The blades are all similar and each is so arranged that the area through which steam leaves is less than the one through which it enters to increase the velocity of the steam.

45. Condenser The function of the condenser is to condense the steam exiting the turbine. The condenser helps maintain low pressure at the exhaust. Two types of condensers are used: Jet and Surface condensers

46. Jet Condenser

47. Jet Condenser

48. Surface Condenser

49. Surface Condenser

50. Cooling Towers & Spray ponds Condensers need huge quantity of water to condense the steam. Roughly 1 Kg of steam needs 100 Kg of cooling water for the condenser. (200MW plant needs 1500*10 6 gallons/day of cooling water) Water is led into the plants by means of circulating water pumps and after passing through the condenser is discharged back into the river. If such a source is not available closed cooling water circuit is used where the warm water coming out of the condenser is cooled and reused. In such cases ponds and cooling towers are used where the water loses heat to the atmosphere. Wet and dry Cooling

51. Wet and Dry Cooling

52. Cooling Towers

53. Feed Water Heater It is necessary to heat water before feeding back to the boiler because: Feed Water heating improve overall efficiency. The dissolved oxygen which would otherwise cause boiler corrosion are removed in the feed water heater. Thermal stresses due to cold water entering the boiler drum are avoided. Quantity of steam produced by the boiler is increased. Some other impurities carried by steam and condensate, due to corrosion in boiler and condenser, are precipitated outside the boiler.

54. Ash handling plant The percentage of ash in coal varies from 5% in good quality coal to about 40% in poor quality coal Power plants generally use poor quality of coal , thus amount of ash produced by it is pretty large A modern 2000MW plant produces about 5000 tons of ash daily The stations use some conveyor arrangement to carry ash to dump sites directly or for carrying and loading it to trucks and wagons which transport it to the site of disposal

55. About 84% of the total ash content of the coal goes with the flue gases in the form of dust or fly ash Remaining 16% drops into the furnace bottom slag hopper in the form of ash lumps formed on the water walls The dust and fly ash contained in the flue gas is collected and separated in electrostatic precipitator whose efficiency is about 98-98.5% There are 2 types of precipitators: Electrostatic precipitator Mechanical cyclone type precipitator

56. The ash collected in this precipitator is either pneumatically moved with air under pressure or vacuumatically up to the main ash silos The furnace bottom slag is either handled by chain or fluidised operation. Belt conveyors and bucket conveyers are used to transport slag ash from boiler bottom hopper to slag silos Dumper is used to dump in the ash dumping site Most reliable, clean and efficient way is ash sluicing system Ash slurry is formed by mixing it with water and discharged from the power station to a suitable valley away from the power station.

57. Electrostatic precipitator Consists of 2 electrodes which are completely insulated from each other High voltage electrostatic field is maintained across them One set is called emitting or discharge electrode which is in the form of thin wires Other set is called collecting electrode The emitting or discharge electrodes are placed in the middle of the pipe in case of tubular type precipitator Or midway between two plates in plate type precipitator

58. The emitter is connected to negative polarity of HVDC source of 25-100kV Collector is connected to positive polarity and is earthed. High electrostatic field is thus set up between both of them which creates corona discharge and ionises the gas molecules as the flue gas flow through the tube or in between the plates The dust particles in the gas acquire negative charge and are attracted towards the collectors and get deposited there The deposited dust is made to fall off the electrodes when rapped mechanically Types of ESP: Horizontal flow or vertical flow type Plate or tubular type Dry or wet type Usually a dry type ESP is employed.

59. Auxiliaries The equipment which help in proper functioning of the plant are called plant auxiliaries. They can be grouped under: Boiler auxiliaries: induced draught fans, boiler feed pumps, secondary air fans, air preheaters, soot blowers , forced and induced draught fans, pulverised fuel, conveyers, feeders, pulverising mills, exhausters, air heaters etc Coal and ash auxiliaries: wagons, tipplers, elevators, skiphoists, conveyers, cranes, pumps, exhausters etc Turbo-alternator auxiliaries: circulating water pumps, condensate extraction pumps, governer control, evaporator, sludge or distillate pumps, ventilating fans, oil pumps, oil purifier, exciter, exciter field, rheostat, turning gear etc Miscellaneous auxiliaries: air compressor, water and fire service pump, workshop machinery and equipments.

60. Essential or continuos auxiliaries: Which are associated with the running of the unit and whose loss would cause an immediate reduction in the output of the unit Draft fans, feed water pumps, circulating water pumps, auxiliary oil pump, ventilating fans, lighting and switch gear, tripping circuits, feeders, etc Non-essential or non continuos auxiliaries: May be put out of operation for sometime and output of the unit may not vary Coal and ash handling plant, service pumps, oil pumps, overhead cranes etc

61. Auxiliary supply features Two main sources of supply From grid via station transformer From main generators through unit transformers Essential auxiliaries supplied from unit transformers, non essential from station transformers For 200MV unit, the rating of unit transformer is 12.5MVA and rating of station transformer is 20MVA. Such a station can provide: Starting load of 1 unit-8MVA Essential load of 1 unit- 8MVA Non essential load of 1 unit -4MVA

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