1. The Process of Bleeding:
Bleeding (also known as steam extraction) involves withdrawing a small percentage of steam from the turbine at intermediate stages before it has completed its full expansion.
• Instead of allowing this steam to expand all the way to the condenser pressure, it is directed to a "feed water heater."
• In the heater, the extracted steam condenses and transfers its latent heat to the high-pressure feed water coming from the pump.
2. Why Bleeding Increases Efficiency: The primary goal of bleeding is to increase the average temperature of heat addition to the cycle.
• By pre-heating the water before it enters the boiler, the boiler has to do less "sensible heating" (heating the water to its boiling point).
• This reduces the external heat input required from the fuel while the reduction in turbine work output (due to the extracted steam) is relatively small.
3. Comparison with Other Terms:
• Compounding: Using multiple stages to reduce the high rotational speed of the turbine.
• Governing: The method of controlling the turbine speed and output power to match the load on the generator.
• Cooling: The general removal of heat, which is not the specific term for this regenerative process.