Air Preheaters for Gas-Fired Boilers in Power Plants

Air preheaters (APHs) are critical components in gas-fired boiler systems. They recover heat from flue gases and transfer it to the incoming combustion air, improving boiler efficiency and reducing fuel consumption.

1. Function of Air Preheaters

• Preheat ambient air before it enters the boiler furnace

• Recover waste heat from flue gases

• Reduce fuel consumption and CO₂ emissions

• Enhance combustion efficiency and reduce thermal shock to the boiler

2. Types of Air Preheaters

1. Rotary (Regenerative) Air Preheaters

• Consist of a rotating heat-absorbing matrix

• Flue gas and air pass through alternate sectors

• Common in large power plants

2. Tubular (Recuperative) Air Preheaters

• Flue gas flows over finned tubes while air flows inside the tubes

• Simple, robust design

• Suitable for smaller boilers or retrofit applications

3. Design Considerations

• Temperature: Flue gas outlet temperature and preheated air temperature

• Flue gas composition: Avoid corrosion from sulfur or other acids

• Pressure drop: Minimize to reduce fan energy consumption

• Material selection: Stainless steel, carbon steel, or corrosion-resistant alloys

4. Benefits of Air Preheaters

• Improves boiler efficiency by 5–15%

• Reduces fuel costs and emissions

• Enables faster startup and stable combustion

• Protects boiler tubes by reducing thermal stress

5. Applications in Gas-Fired Power Plants

• Combined-cycle gas turbines (CCGT)

• Industrial gas-fired boilers

• District heating and cogeneration plants

• Retrofitting older boilers for improved efficiency

6. Maintenance Tips

• Regular inspection for fouling and corrosion

• Cleaning of air and gas passages to maintain heat transfer

• Monitoring of bearings and seals in rotary types

• Ensure proper flue gas bypass in regenerative APHs

Summary

Air preheaters are essential for energy efficiency and environmental compliance in gas-fired power plants. By recovering waste heat from flue gases, they reduce fuel consumption, improve combustion, and extend boiler life, making them a vital component of modern thermal power generation systems.