In today’s industrial and power-generation boilers, energy efficiency is no longer optional—it is a necessity. One of the most important heat recovery devices used to improve boiler performance is the Air Preheater (APH). The proper use of APH in boiler systems helps reduce fuel consumption, increase thermal efficiency, and improve combustion stability.
Durga Boilers & Engineering Works design and supply high-quality boiler components, including advanced air preheater systems, engineered for long-term reliability and performance. This blog explains what air preheaters are, how they work, their functions, benefits, types, and applications in simple yet technical language.
What is Air Preheaters (APH)?
An air preheater is a heat exchange equipment installed in the path of boiler flue gases. It transfers heat from hot exhaust gases to the incoming combustion air before the air enters the furnace. The APH full form in boiler is Air Preheater. In simple terms, APH in boiler systems reuse waste heat to preheat air, instead of allowing it to escape through the chimney. Air preheaters are widely used in:
- Industrial boilers
- Power plant boilers
- Process steam generation units
They are especially essential in large installations such as an air preheater in thermal power plant, where even small efficiency improvements result in major fuel savings.
Working of Air Preheaters (APH)
The working principle of an air preheater is based on indirect heat transfer between hot flue gas and cold combustion air.
Step-by-Step Working Process:
- Hot flue gases exit the boiler after combustion.
- These gases pass through the air preheater section.
- Cold atmospheric air flows on the opposite side of the heat transfer surface.
- Heat from flue gases is transferred to the incoming air.
- Preheated air is supplied to the boiler furnace.
- Cooler flue gases are released through the chimney.
This process improves combustion efficiency and reduces stack heat losses. In large boilers, especially in an air pre heater in thermal power plant, this heat recovery is critical for plant performance.
What is the Function of the Air Preheater?
The primary function of an air preheater is to improve boiler efficiency by recovering waste heat. However, it also performs several supporting roles. Main Functions of Air Preheater:
- Preheating combustion air
- Improving fuel ignition and flame stability
- Reducing fuel consumption
- Lowering flue gas exit temperature
- Enhancing boiler thermal efficiency
These functions make APH in boiler systems an essential component for efficient steam generation.
What is the Function of the Air Preheater in Boiler?
Specifically in a boiler system, the air preheater ensures that air entering the furnace is already warm. This reduces the energy required to raise air temperature during combustion. The function of air preheater in boiler includes:
- Increasing overall boiler efficiency
- Reducing unburnt fuel losses
- Improving heat transfer inside the furnace
- Supporting consistent and stable combustion
Without an air preheater, a boiler loses a significant amount of usable energy through hot exhaust gases.
Why Is Hot Air Sent to the Furnace?
Sending hot air to the furnace improves the combustion process.
Key Reasons:
- Hot air enhances fuel-air mixing
- Fuel ignites faster and burns more completely
- Less fuel is required to maintain furnace temperature
- Flame stability improves
In coal-fired units and large boilers, especially in an air preheater in thermal power plant, hot air is critical for efficient combustion and load stability.
Benefits of Using an Air Preheater
Using an air preheater in boiler systems offers several operational and economic benefits.
- Improved Thermal Efficiency- Recovered heat from flue gases increases boiler efficiency by a significant margin.
- Fuel Savings- Preheated air reduces the amount of fuel required to reach combustion temperature.
- Reduced Operating Cost- Lower fuel consumption directly reduces operating and maintenance costs.
- Lower Emissions- Efficient combustion reduces carbon monoxide and particulate emissions.
- Increased Boiler Capacity- Better heat utilization allows higher steam generation without additional fuel input.
Different boiler capacities and fuel types require different air preheater designs.
Type of Air Preheaters (APH)
Recuperative Air Preheater
Heat transfer occurs continuously through stationary surfaces.
Features:
- Simple design
- Used in small and medium boilers
- Low maintenance
Regenerative Air Preheater
Uses a rotating heat storage element.
Features:
- High efficiency
- Commonly used as air preheater in thermal power plant
- Suitable for large boilers
Tubular Air Preheater
Consists of tubes through which air or flue gas flows.
Features:
- Robust construction
- Suitable for coal and oil-fired boilers
Plate Type Air Preheater
Uses metal plates arranged in parallel.
Features:
- Compact design
- Used in limited-space installations
Applications of Air Preheaters
Air preheaters are used in a wide range of industries due to their energy-saving benefits.
Industrial Boilers used in Chemical plants, Textile industries, Food processing units.
Thermal Power Plants
The air pre heater in thermal power plant improves heat rate and reduces coal consumption.
- Cement & Steel Industries
- Used in high-temperature process heating systems.
- Refineries & Petrochemical Plants
- Supports efficient combustion in heaters and boilers.
Materials Used in Air Preheaters
Air preheaters operate under high temperature and corrosive conditions. Common materials include:
- Carbon steel
- Alloy steel
- Corrosion-resistant coatings
- High-temperature seals
Material selection depends on fuel type and flue gas composition.
Maintenance of Air Preheaters
Proper maintenance ensures long service life and consistent performance:
- Regular cleaning of heat transfer surfaces
- Monitoring pressure drop and leakage
- Checking seals, bearings, and rotating elements
- Preventing ash accumulation
Conclusion
Understanding what is air preheaters in boiler (APH), their working, functions, types, and benefits is essential for improving boiler efficiency. An air preheater recovers waste heat, reduces fuel consumption, and enhances combustion performance.
Whether in an industrial boiler or an air preheater in thermal power plant, APH systems play a vital role in energy-efficient operations. For dependable and high-quality air preheaters, Durga Boilers & Engineering Works stands as a reliable steam boiler industry partner.
