What is regenerative feedwater heating and how does it improve boiler efficiency?

What is regenerative feedwater heating and how does it improve boiler efficiency?

• A. Preheating feedwater using exhaust or steam pressure before entering the boiler, reducing the fuel needed to generate steam.
• B. Directly heating feedwater with electric heaters after the boiler.
• C. Cooling feedwater before it enters the boiler to reduce temperature.
• D. Preheating feedwater using ambient air in a cooling coil outside the boiler.

Answer: (D)

Regenerative feedwater heating uses heat recovered from the steam turbine exhaust to raise the temperature of the feedwater before it enters the boiler. In a typical steam cycle, some high-energy steam is taken from the turbine (bleed steam) or exhaust steam is routed through a feedwater heater and transfers its heat to the incoming feedwater. This preheating means the boiler now has to add less energy to turn water into steam, so the fuel consumed for the same steam output is reduced. The result is higher overall cycle efficiency and better energy use. It also helps smoother heat transfer and lowers thermal stress on boiler components by tempering the feedwater temperature rise. The alternative methods described—heating after the boiler with electric heaters, cooling or cooling with ambient air outside the boiler—do not recover waste heat and would waste energy or be impractical, which is why they do not improve boiler efficiency in the same way.

Regenerative feedwater heating uses heat recovered from the steam turbine exhaust to raise the temperature of the feedwater before it enters the boiler. In a typical steam cycle, some high-energy steam is taken from the turbine (bleed steam) or exhaust steam is routed through a feedwater heater and transfers its heat to the incoming feedwater. This preheating means the boiler now has to add less energy to turn water into steam, so the fuel consumed for the same steam output is reduced. The result is higher overall cycle efficiency and better energy use. It also helps smoother heat transfer and lowers thermal stress on boiler components by tempering the feedwater temperature rise. The alternative methods described—heating after the boiler with electric heaters, cooling or cooling with ambient air outside the boiler—do not recover waste heat and would waste energy or be impractical, which is why they do not improve boiler efficiency in the same way.