Air Preheaters (Air Preheater – LUVO) and the Application of Acoustic Cleaning: Importance for Energy Efficiency and Safe Operation
Abstract
In industrial energy production systems, air preheaters (LUVO – Luftvorwärmer) play a key role in enhancing boiler efficiency by preheating combustion air using hot flue gases. Especially in solid-fuel boiler systems, preheated combustion air enables more effective combustion and reduces fuel consumption. This article discusses the fundamental operating principles of air preheaters, their role in energy recovery, and the contribution of acoustic cleaning technology in maintaining their performance.
1. Basic Principle of Air Preheaters and Energy Recovery
Air preheaters are used in energy production facilities to recover part of the waste heat from hot flue gases exiting boilers, in order to preheat the fresh air used for combustion. This application increases both combustion efficiency and overall system efficiency. Typically, for every 50°C increase in air temperature, approximately 2.5% fuel savings can be achieved [[1]].
Flue gas temperatures generally exceed 200°C, making them economically viable for heat recovery. The heated air can be used for the following purposes:
Preheating combustion air for the boiler,
Supporting process air (drying, cooking, heating, etc.),
Heating nearby rooms such as boiler houses.
2. Contribution of Air Preheaters to Efficiency
The use of an air preheater provides the following benefits:
- Efficiency gain: Depending on the flue gas outlet temperature, facility efficiency can improve by 3–7%.
- Reduced fuel consumption: Less fuel is required to produce the same thermal output.
- Improved combustion quality: In solid-fuel boilers, using preheated combustion air between 150–320°C increases furnace temperature, enhances radiation heat transfer, and improves combustion quality.
These advantages make air preheaters a priority engineering solution, especially in medium- and large-capacity solid fuel boilers.
3. Heat Transfer and Limiting Factors
The efficiency of heat transfer between air and flue gas increases as the temperature difference increases. Therefore:
The temperature of the flue gas entering the air preheater (typically 200–400°C),
The temperature of the heated air (typically 150–320°C),
And the outlet gas temperature should be optimized to ensure maximum heat recovery.
However, a critical limiting factor is that the heat transfer coefficient of air is lower than that of water. As a result, air preheaters require a larger surface area, which increases the risk of ash accumulation [[2]].
4. Ash Accumulation in Air Preheaters and Acoustic Cleaning
When solid fuels such as pulverized coal are used, the flue gas carries a high load of fly ash. These particles accumulate on the surfaces of the air preheater over time, resulting in:
- Reduced heat transfer efficiency,
- Obstruction of air passages,
- Increased risk of fire due to combustible dust particles igniting in hot air.
The ignition of dust particles in hot air can lead to severe equipment damage. Therefore, regular removal of ash buildup is critical to ensure safe and efficient operation.
Özellikle sıcak hava içerisinde yanıcı tozların tutuşması, önemli malzeme hasarlarına yol açabilir. Bu nedenle, hava ısıtıcılarında kül birikiminin periyodik olarak giderilmesi kritik önemdedir.
4.1. Application of Acoustic Cleaning
Acoustic cleaners generate high-energy sound waves in the 60–300 Hz range, which cause accumulated particles on heat exchange surfaces to vibrate and detach. The dislodged particles are then carried away by the gas stream. This technology is also applied in air preheaters and offers the following benefits:
- Non-damaging to surfaces,
- Operates during process conditions,
- Resistant to high temperatures,
- Low energy consumption.
These systems, developed by domestic companies such as User Mühendislik, are increasingly adopted as a preventive maintenance strategy, particularly in applications with high ash loading [[3]].
5. Conclusion and Recommendations
Air preheaters are indispensable equipment in industrial boilers for both energy recovery and combustion quality. However, long-term use may result in ash accumulation, leading to reduced efficiency and increased fire risk. Therefore, it is recommended to:
- Integrate acoustic cleaning systems,
- Establish periodic inspection and cleaning protocols,
- Monitor temperatures to mitigate the risk of combustible particles.
These practices ensure safe and high-efficiency operation of air preheaters in industrial energy systems.
References
- H.C. Saxena, Thermal Engineering, 2004.
- Boysan, F., & Tarman, M. (2012). The Role of Air Preheaters in Energy Recovery. Journal of HVAC Engineering (Tesisat Mühendisliği Dergisi).
- Andersson, H. et al. (2014). Use of Acoustic Cleaning in Heat Recovery Systems. Chemical Engineering & Technology.
- USER Mühendislik. (2023). Sonic Soot Blower Systems Catalog.
