comparison between economizer and airpreheater

Economizer vs. Air Preheater: A Detailed Comparison for Boiler Efficiency

Boiler systems often employ auxiliary heat recovery devices to improve efficiency and reduce fuel consumption. Two of the most common components are the Economizer and the Air Preheater (APH). While both serve the purpose of utilizing waste heat from flue gases, their functions, impact on efficiency, and maintenance requirements differ significantly. Let’s explore a detailed comparison.  

🔥 Efficiency

- Economizer: Primarily increases the temperature of feed water before it enters the boiler. By preheating the water, the boiler requires less fuel to convert it into steam, thereby improving overall thermal efficiency.  

- Air Preheater (APH): Raises the temperature of combustion air supplied to the furnace. Warmer air enhances fuel combustion, leading to better flame stability and improved boiler efficiency.  

⚙️ Corrosion in Boiler

- Economizer: Boiler corrosion is often caused by dissolved oxygen and other gases in feed water. As the economizer heats the water, these gases are released, reducing the risk of corrosion. Thus, the economizer indirectly helps in minimizing boiler corrosion.  

- Air Preheater (APH): Simply heating combustion air does not address corrosion issues. Corrosion in APH surfaces can still occur due to acidic condensates formed at low flue gas temperatures, especially when burning high-sulfur fuels.  

🌍 Effect of Ambient Conditions

- Economizer: Ambient conditions have no direct effect on its performance since it deals with feed water inside a closed system.  

- Air Preheater (APH): Performance is influenced by atmospheric conditions. Variations in ambient temperature and humidity affect the density and volume of combustion air, which in turn impacts boiler efficiency.  

💰 Repairing & Maintenance Cost

- Economizer: Generally involves higher maintenance costs due to its complex design, higher operating pressures, and susceptibility to scaling or fouling from feed water impurities.  

- Air Preheater (APH): Comparatively lower maintenance costs, as its design is simpler and it handles air rather than water. Cleaning and inspection are relatively easier.  

📊 Heat Transfer Coefficient

- Economizer: Exhibits a higher heat transfer coefficient ranging between 50 to 300 W/m²·°C, making it more effective in transferring heat from flue gases to feed water.  

- Air Preheater (APH): Has a lower heat transfer coefficient in the range of 10 to 50 W/m²·°C, which means its heat recovery efficiency is comparatively less.  

📌 Conclusion

Both Economizers and Air Preheaters play vital roles in enhancing boiler efficiency, but they serve different purposes. Economizers are more effective in heat transfer and corrosion control, though they come with higher maintenance costs. Air Preheaters, on the other hand, improve combustion efficiency at a lower cost but are more sensitive to ambient conditions.  

For industries aiming at maximum energy recovery, a combination of both devices is often employed to achieve optimal boiler performance.