Thermal Power Plants

Overview

• Thermal power plants meet about half of the world's power demand.
• Use water as the working fluid.
• Operate under green efficiency, conforming to environmental standards.

Coal-Based Thermal Power Plant Operation

1. Electricity Generation

   • The generator produces electricity by turning a shaft driven by a steam turbine.
   • The steam turbine is the heart of the power plant.

2. Steam Supply

   • High pressure and high temperature steam is required at the turbine's inlet.
   • As steam passes through the turbine, its pressure and temperature drop.

3. Steam Turbine Design

   • Often consists of multiple stages: high pressure, intermediate pressure, and low pressure turbines.

4. Cycle Recirculation

   • To repeat the process, low pressure and low temperature steam must return to high pressure and temperature.

Steps for Recirculation

• Raising Pressure

  • Instead of compressing steam (energy-intensive), steam is condensed into liquid.
  • Condenser Heat Exchangers
    • Cold water flows through tubes, absorbing heat from steam, causing it to condense.
    • A pump increases the pressure of the condensed water (feed water).

• Raising Temperature

  • A boiler is used to add heat to the exit of the pump.
  • Water Tube Boiler
    • Pulverized coal is burned inside.
    • Water passes through an economizer to capture energy from flue gases, then transforms into steam.
  • Steam is separated at the steam drum, returning to original high pressure and temperature state.

Improving Efficiency

• Basic Rankine Cycle

  • Basic cycle has low efficiency.

• Superheating

  • Additional heat after steam conversion increases efficiency; limited to 600°C for turbine material durability.

• Reheating

  • Adding heat after the first turbine stage increases steam temperature for higher power output.

• Feed Water Heater

  • Prevents boiler material degradation by removing dissolved gases in feed water.
  • Hot steam from the turbine mixed into feed water absorbs gases and preheats it, improving efficiency.

Efficiency Range

• Modern power plants operate at an efficiency of 40-45%.

Heat Addition and Rejection

• Cooling Tower

  • Supplies cold liquid to the condenser.
  • Heated water is sprayed in the cooling tower, inducing air draft to lose heat.

• Pollutant Management

  • Exhaust gases from burning coal are treated in an Electrostatic Precipitator (ESP) before release.
  • ESP uses high voltage static electricity to capture pollutant particles.

Conclusion

• Understanding these processes enhances insight into the workings of thermal power plants.