Power Engineering II. Technological circuits of thermal power plants

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1 Technological circuits of thermal power plants

2 Lay out scheme of coal power plant climatetechwiki.com Technological circuits 2

3 Coal and ash circuit Air and gas circuit Feed water and steam circuit Cooling water circuit Technological circuits 3

4 Coal circuit Coal Lignite youngest brown coal, energy value circa MJ/kg Brown coal energy value MJ/kg (sulfur content 0,5-4,5%, ash content 30-45%) Black coal energy value MJ/kg Anthracite best quality coal, energy value 26-30MJ/kg Technological circuits 4

5 Coal circuit - boilers Boilers with grate furnace Moving grate Worst coal burning on grate Rocking grate bars Pulverized boilers Combustion of coal dust fueled by compressed air into the furnace, coal dust and compressed air are mixtured in burners Better coal burning, wide control range (min power 30% of rated power) Necessary coal milling Higher requirements to fly ash separation Technological circuits 5

6 Coal circuit burners configurations Technological circuits 6

7 Coal circuit - boilers Cyclone furnace Vortex field -> high speed between air and burned grain Combustion of a low quality fuel Combustion of coarse-grained fuel -> saving of milling work Vertical or horizontal arrangement Technological circuits 7

8 Coal circuit - boilers Fuel Secondary air Tangential inlet of secondary air Terciary air Cinder outlet Technological circuits 8

9 Coal circuit - boilers Fluidized bed combustion Combustion of grained fuel in fluidized bed which is created by vertically jets of air Gradually burning grains of fuel get into higher layers, in the final phase they are carried out by a flow of exhaust out from a furnance Combustion of fuel with low energy value, SO x caption by adding of crushed limestone, lower NOx production due to lower temperature Technological circuits 9

10 Coal circuit - boilers Exhaust input to cyclone Cyclone Coal and limestone feed Fluidized bed Boiler with stationary fluidized bed Coal and limestone feed Fluidizing air Fluidized bed Fluidized bed boiler with cyclone Bed material return Fluidizing air Technological circuits 10

11 Downcomer tube Feed water and steam circuit Steam drum boiler Steam drum Superheater Water heater Water tubes Feed pump Technological circuits 11

12 Feed water and steam circuit Steam drum is a gravitational water and saturated steam separator Natural water circulation is caused by density difference of heated water in water tubes and nonheated water in downcomer tubes High hot water accumulation inside a steam drum improve control possibilities of boiler, the higher mass flow can be delivered for a short while than it would correspond to the instantaneous boiler output Technological circuits 12

13 Feed water and steam circuit High pressure boiler (Benson) Superheater Evaporator Economiser Feed pump Technological circuits 13

14 Feed water and steam circuit Water flow is given by output pressure of feed pump There are no fixed borders between heating, evaporating and superheating parts of boiler Control of high pressure boiler is more difficult due to the low accumulation ability (faster starting and shutting down the boiler) Technological circuits 14

15 Steam turbines Impulse turbines Steam expansion occurs in stator nozzles and all hydraulic energy is converted into kinetic energy c Fixed stator nozzle Steam velocity c Steam pressure Rotor Rotation Technological circuits 15

16 Steam turbines Reaction turbine Steam expansion occurs in both stator and rotor nozzles c Steam velocity c c Steam pressure p Stator Rotation Rotating nozzle Technological circuits 16

17 Steam turbines Technological circuits 17

18 Steam turbine governing Throttle governing The pressure is reduced at the turbine input loss of energy Control valve throttling Loss of enthalpy difference Technological circuits 18

19 Steam turbine governing Nozzle governing The steam is regulated by opening or closing of sets of nozzles V V throttling NS NS V NS NS V Further expansion V. Valves NS Nozzle sets Technological circuits 19

20 Cooling water circuit Condenser Steam Water outlet Cooling water inlet Condensate Technological circuits 20

21 Cooling water circuit PCW Once-through cooling system PCW Recirculating cooling system PCW Pump of cooling water Technological circuits 21