Monday, September 21, 2009

How a Coal-fired Power Plant works

Coal Fired Power Plant Process

1. Coal Supply

  • Coal from the mine is delivered to the coal hopper, where it is crushed to five centimetres (2 inches) in size.
  • The coal is processed and delivered by a conveyor belt to the generating plant.

2. Pulverizer

  • The coal is then pulverized, or crushed, to a fine powder, mixed with air and blown into the boiler, or furnace for combustion.

3. Boiler

  • The coal / air mixture ignites instantly in the boiler.
  • Millions of litres of purified water are pumped through tubes inside the boiler.
  • Intense heat from the burning coal turns the purified water in the boiler tubes into steam, which spins the turbine (see number four) to create electricity.

4. Precipitator, stack

  • Burning coal produces carbon dioxide (CO2), sulphur dioxide (SO2) and nitrogen oxides (NOx).
  • These gases are vented from the boiler.
  • Bottom ash, which is made of coarse fragments that fall to the bottom of the boiler, is removed.
  • Fly ash, which is very light, exits the boiler along with the hot gases.
  • An electrostatic precipitator (a huge air filter) removes 99.4 per cent of fly ash before the flue gases are dispersed into the atmosphere.

5. Turbine, generator

  • Water in the boiler tubes picks up heat from the boiler and turns into steam.
  • The high-pressure steam from the boiler passes into the turbine (a massive drum with thousands of propeller blades).
  • Once the steam hits the turbine blades, it causes the turbine to spin rapidly.
  • The spinning turbine causes a shaft to turn inside the generator, creating an electric current.

6. Condensers and the cooling water system

  • Cooling water is drawn into the plant and circulated through condensers, which cools steam discharged from the turbine.
  • Steam from the turbine also passes through the condensers in separate pipes from cooling water.
  • The cold water is warmed by the steam, which condenses back into pure water and circulates back to the boiler to begin the process of generating electricity again.
  • Cooling water, now warm from the heat exchange in the condensers, is released from the plant.

7. Water treatment plant: water purification

  • To reduce corrosion, water must be purified for use in the boiler tubes.
  • Other wastewater systems within the plant collect water used to clean pipes and other equipment, and sludge from the water purification process and other processes.
  • Waste water is pumped out of the plant and into the holding ponds.

8. Precipitator, Ash systems

  • Ash that builds up on the precipitator's plates is vibrated off and collected in large hoppers or bins.
  • Fly ash and bottom ash are removed from the plants and hauled to disposal sites or ash lagoons.
  • Depending on the market demand, fly ash produced from TransAlta's three plants is sold to the cement industry for construction.

9. Substation, transformer, transmission lines

  • Once the electricity is generated, transformers increase the voltage so it can be carried across the transmission lines.
  • Once electricity is delivered to substations in cities and towns, the voltage flowing into the distribution lines is reduced, and then reduced again to distribute electricity to customers.
Source: canadiancleanpowercoalition
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