1 SUBJECT CODE SUBJECT NAME STAFF NAME : ME8792 : Power Plant Engineering : Prof.V.Tamil Selvi Ms.P.Aileen Sonia Dhas
2 UNIT- I COAL BASED THERMAL POWER PLANTS Rankine cycle - improvisations, Layout of modern coal power plant, Super Critical Boilers, FBC Boilers, Turbines, Condensers, Steam & Heat rate, Subsystems of thermal power plants Fuel and ash handling, Draught system, Feed water treatment. Binary Cycles and Cogeneration systems
3 RANKINE CYCLE Rankine cycle is a thermodynamic cycle on which the steam turbine works. The line diagram is shown in fig.
4 Thermal Efficiency of Rankine Cycle
5 P-V Diagram
6 T-S Diagram
7 Improvisations of Rankine Cycle Rankine cycle efficiency can be improved by using the following three methods. 1. Reheating 2. Regeneration 3. Combined reheating and regeneration
8 Reheat Rankine Cycle The efficiency of the simple Rankine cycle can be improved by increasing the pressure and temperature of steam entering into the turbine and keeping the steam as dry as possible at the end of turbine.
11 T-S Diagram
12 Regenerative Rankine Cycle The Condensate coming out of the turbine is heated with the help of steam in a reversible manner. This type of heating is known as regenerative heating.
14 Practical single stage regenerative Rankine cycle
15 T-S Diagram
16 Reheat-Regenerative Cycle
17 T-S Diagram
18 Layout of modern coal power plant A steam power plant converts the chemical energy of the fossil fuels (coal, oil, gas) into mechanical / electrical energy. Coal based thermal power plant are meant for base load requirements. The following two purposes can be served by a steam power plant. To produce electric power. To produce steam for industrial purposes besides producing electric power.
19 The layout of modern steam power plant comprises of four main circuits namely Coal and ash circuit Air and gas circuit Feed water and steam flow circuit Cooling water circuit
22 Advantages They respond rapidly to the load variations without difficulty. Can be located very conveniently near to load centre. Transmission cost is reduced. Less space is required compared to hydel power plants Cheaper in production and initial cost compared to diesel power stations.
23 Disadvantages Maintenance and operating cost are high. Plant construction time is more. Very large quantity of water is required. Coal handling is a tedious process.
24 BOILERS A boiler is a closed vessel in which the steam is generated from water by applying heat. A boiler or steam generator is used where a source of steam is needed. The boilers are mainly used in mobile steam engines such as Steam locomotives Portable engines Steam powered road vehicles Industrial installations Power stations
25 Types of Boilers Fire tube boiler If the hot gas is passed through tubes and the water is circulated around tubes, it is called fire tube boiler. Examples: Cochran boiler and Locomotive boiler Water tube boiler If the water is circulated through a large number of tubes and the hot gases pass around the tubes, it is called water tube boiler. Examples: Babcock and Wilcox boiler Low pressure and High pressure boiler Low pressure boiler: Steam pressure range from 3.5 to 10 bar. Example: Cochran boiler High pressure boiler: Steam pressure greater than 25 bar and temperature of 500 o C. Examples: Babcock and Wilcox boiler
26 ONCE THROUGH BOILER In once through boiler if the water is fed to the boiler, it will be fully converted into dry or superheated steam without any water content present in it. Advantages Easy control of steam temperature. Easy to adopt variable pressure operation. Starting and cooling down of the boilers is fast. It is smaller in size and weighs less.
28 FLUIDIZED BED COMBUSTION BOILERS (FBC BOILERS) When a gas is passed through a packed bed of finely divided solid particles, it experiences a pressure drop across the bed. When the velocity of the gas is increased further, at a stage the particles get suspended in the gas stream and the new packed bed becomes a fluidized bed. Burning of a fuel in such as state is known as fluidized bed combustion.
30 Advantages of FBC boilers Size is small hence capital costs are reduced. Responds rapidly to changes In load demand. Less pollution. Combustion temperature can be controlled accurately.
31 TYPES OF FBC 1. Bubbling Fluidized Bed Boilers (BFB)
32 2. Circulating Fluidized Bed Boilers (CFB)
40 Functions of condenser
41 Elements of condenser
42 Classification of condenser
43 Surface condenser
45 Down flow surface condenser
46 Central flow surface condenser
47 Low level parallel flow
48 Low level counter flow
49 Parallel and counter flow
50 Ejector condenser
51 Evaporative condenser
53 SUBSYSTEMS OF THERMAL POWER PLANTS a) Fuel and Ash Handling b) Draught system c) Feedwater treatment d) Binary cycles and Cogeneration systems
54 A)COAL HANDLING OUT PLANT HANDLING transport to Stations by sea/river, rail, road, ropeways, pipelines. IN PLANT HANDLING Coal Preparation Transfer of coal and related equipments Belt Conveyors Screw conveyors Bucket elevators Grab bucket conveyor Covered storage and required equpments Inplant handling of coal Coal weighig measures.
62 ASH HANDLING i. Mechanical Handling System ii. Hydraulic Ash handling System iii. Pneumatic Ash handling System iv. Steam Jet System
64 i.mechanical handling System In this system, ash cooled by water seal falls on the belt conveyor and is carried out continuously to the bunker. The ash is then removed to the dumping site from the ash bunker with the help of trucks
66 ii)hydraulic system
67 iii.pneumatic Ash Handling System In this system, ash from the boiler furnace outlet falls into crusher The ash is then carried by high velocity air or steam to the point of delivery Air leaving the ash separator is passed through filter to remove dust etc., so that the exhauster handles clean air which will protect the blades of the exhauster.
68 iv) Steam Jet system
69 c)draught SYSTEM The purpose of draught is to supply required quantity of air for combustion and remove the burnt products from the system. Draught Natural Draught Artificial Draught Forced Draught Induced Draught Balanced Draught- Forced draught+induced Draught
70 FORCED DRAUGHT
71 Draught produced by chimney is due to the temperature difference of hot gases in the chimney and cold air outside the chimney.
72 Induced Draught
73 In this blower is located near the base of chimney instead of grate. The air is sucked in the system by reducing the pressure throught the system below atmospheric pressure.
74 BALANCED DRAUGHT
75 FEED WATER TREATMENT
76 Feed water
77 Binary cycle
78 It is one type of combined cycles in which usually two working fluids mercury and water are used to improve the overall thermal efficiency of the power plant. For getting best performance of vapour power cycle, the working fluid should have the following characteristics» High enthalpy of vaporization» High critical temperature with a low corresponding saturation temperature.» Freezing temperature should be below room temperature.» High condenser temperature
79 Low specific heat Chemically stable Good heat transfer characteristics The moisture should not appear during expansion