What is Air Preheaters (APH)
Air Preheaters (APH) are the Shell and tube type Heat Exchangers used for preheating the air which is fed to the boiler or furnaces/kilns for combustion of fuels. The Air Pre heater’s primary objective is to extract the waste heat from the flue gases leaving the boiler.
Thermodyne Engineering Systems manufacture Air Preheaters which are given as a standard side accessory along with the main equipment – Boiler, in a Packaged Type Boiler, Combi Boilers.
What is the function of the air preheater?
The primary function of an air preheater (APH) is to enhance the thermal efficiency of a boiler system by utilizing the waste heat from flue gases to preheat the air entering the combustion chamber. By raising the temperature of the incoming air, the APH reduces the energy required to ignite and sustain the combustion process. This results in improved fuel combustion, lower fuel consumption, and reduced flue gas emissions. Overall, the air preheater contributes significantly to optimizing boiler performance, ensuring energy savings, and supporting environmentally efficient steam generation.
Benefits of using an air preheater
- Increases boiler efficiency
- Reduces fuel consumption
- Lowers emissions
- Supports sustainable and energy-efficient operations
- Lowers operating costs and offers quick ROI
- Reduces flue gas temperature and heat loss
- Lowers emissions (CO₂, CO, NOx)
- Increases boiler efficiency by 2–3%
Applications of air preheaters
Power Plants – Enhances boiler efficiency and reduces fuel consumption in large-scale thermal power generation.
Industrial Steam Boilers – Improves energy recovery in manufacturing plants using steam for processes.
Chemical & Pharmaceutical Industry – Ensures consistent heating and controlled combustion for process stability.
Food & Beverage Processing – Maintains energy efficiency in steam-based sterilization and cooking systems.
Plywood & Wood Industry – Helps in drying operations by improving boiler heat output.
Textile Industry – Enhances thermal efficiency in dyeing and drying processes.
Paper & Pulp Industry – Optimizes steam generation required for pulping and paper drying.
Sugar & Distillery Units – Supports efficient combustion of bagasse and other biomass fuels.
Commercial Boilers (Hotels, Hospitals, etc.) – Lowers energy bills and supports green building norms.
Cement & Kiln Operations – Preheats air for fuel combustion in rotary kilns and dryers.
What is the function of the air preheater in boiler ?
An air preheater is a crucial component in boiler systems, primarily responsible for enhancing the boiler’s efficiency. It achieves this by preheating the combustion air before it enters the boiler furnace, leading to several benefits:
- Reduced fuel consumption: Preheating the combustion air significantly reduces the amount of fuel needed to reach the desired boiler temperature. This translates into lower fuel costs and a more environmentally friendly operation.
- Improved combustion efficiency: By supplying preheated air, the combustion process becomes more efficient, leading to a more complete fuel burn. This results in higher heat release and better overall boiler performance.
Why is hot air sent to the furnace?
For generating fire in a boiler furnace 3 main ingredients are needed: Fuel, Air & Ignition. Air is used in a Boiler for the combustion of fuel. Based on the stoichiometry calculation, the right quantity of air along with excess air is fed into the boiler furnace for the combustion of fuel.
Generally, fuel fed to the boiler is at normal room temperature, and for the combustion of fuel to take place; the temperature of the fuel is increased from its room temperature to ignition temperature. So to increase the efficiency of the combustion process as well as a boiler, hot air is fed to the furnace for the combustion of fuel.
Type of Air Preheaters (APH)
We manufacture different types of air preheaters:-
- Shell and tube type single pass air pre-heaters
- Shell and tube-type dual-pass air pre-heaters
- Finned tube air pre-heaters
Working of Air Preheaters(APH)
Air Preheaters have a shell and tube type construction where exhaust heat from the flue gases is transferred to the air when they come in indirect contact with each other.
Air Preheaters consist of a shell where tubes are arranged in a square or triangular pitch and are welded to a tube plate. Depending upon the type of operation and ease of cleaning, flue gases & air can be allowed to travel either shell side or tube side interchangeably.
Also Read: What is Combi Boiler?
Thermodyne Boilers finned tube air preheaters are designed to maximize efficiency by increasing the heating surface area without increasing the space requirement.
Thermodyne Engineering Systems manufacture air preheaters that are tailor-made to suit the customer’s requirement.
Our Air Preheaters are designed in both 1 and 2 passes for both flue gases and air to extract maximum heat from the flue gases.
Thermodyne Boilers manufacture air pre-heaters for a wide capacity range and can satisfy the various fuel requirements of a customer such as:
- Wood
- Coal
- Husk
- Bagasse
- Petcoke
- Light Oil and Heavy Oil
Air Preheater Pros
- 2 pass design to extract maximum waste heat from flue gases leaving the boiler.
- It is used to extract waste heat from the flue gases leaving the boiler exhaust thereby increasing the efficiency of a boiler by 2-3 %.
- It is used to preheat the fuel which further increases the boiler efficiency.
- Payback time is less.
Air Preheater Cons
Adding equipment or accessory in the path of flue gases increases flue gas pressure drop down the line, so the size of the Induced Draft Fan increases.
Buy Air Preheater from Indian Manufacturer: Thermodyne Engineering Systems: Contact Us
Other Industrial Steam Boiler Ancillaries
You can also visit my YouTube Channel: Thermodyne Boilers
Boiler Resources page Link Below
Adding equipment or accessory in the path of flue gases increases flue gas pressure drop down the line, so the size of the Induced Draft Fan increases.
Buy Air Preheater from Indian Manufacturer: Thermodyne Engineering Systems: Contact Us
Other Industrial Steam Boiler Ancillaries
You can also visit my YouTube Channel: Thermodyne Boilers
Air Preheater related FAQs:-
An APH is a heat exchanger that is used to preheat the air that is used to burn fuel in a boiler. This preheating increases the efficiency of the boiler by reducing the amount of fuel that is needed to heat the air.
Increases boiler efficiency by 2–3%
Reduces fuel consumption
Improves combustion performance
Lowers flue gas temperature
Cuts down emissions
Speeds up steam generation
Short payback period
Supports low-grade fuels like husk and bagasse
Yes. At Thermodyne Engineering Systems, air preheaters are provided as a standard accessory with our packaged boilers and combi boiler systems for enhanced performance and energy savings.
Yes. Thermodyne Boilers manufactures customized APH units compatible with multiple fuels such as coal, wood, husk, bagasse, petcoke, and heavy oils, ensuring optimal performance for diverse industrial needs.
Yes, slightly. Since the APH is installed in the path of flue gases, it can cause a pressure drop, requiring a higher-capacity Induced Draft (ID) fan. However, this is offset by the fuel and efficiency gains.
Common types include:
Shell and Tube Type – Single Pass
Shell and Tube Type – Dual Pass
Finned Tube Air Preheaters
Each type is selected based on the application, space, and performance requirements.
By recovering waste heat from the exhaust flue gases and transferring it to the incoming combustion air, the air preheater reduces the energy needed to ignite and burn fuel. This results in a 2–3% increase in boiler efficiency.
The most common problems with air preheaters include:
- Fouling.
- Leaks.
- Damage to the heat exchanger or rotating wheel.
