Analysis of Fan Types and Functions in Tunnel Kilns

1. Forced Draft Fans

(1) Function: Provide continuous combustion air to the kiln, ensuring sufficient oxygen and stable combustion. By generating positive pressure, the fan delivers air into the firing zone to control temperature and atmosphere, thereby improving combustion efficiency and product quality.
(2) Common Types: Centrifugal or backward-curved fans with high-temperature and anti-corrosion properties, adaptable to kiln temperatures up to 800–2000 ℃.

2. Induced / Exhaust Fans
(1) Function: Extract waste gases and vapor from the kiln, maintain negative pressure and stable airflow, improve combustion and drying conditions, and enhance workplace safety and comfort.
(2) Common Types: Centrifugal fans, effective in guiding high-temperature flue gas out of the kiln.

3. Drying / Dehumidification Fans
(1) Function: Used in the drying section of tunnel kilns to remove vapor released from green bricks during dehydration, promoting drying efficiency. Usually axial flow fans with features of large air volume, low pressure (generally less than 300 Pa), and high efficiency.

4. Cooling Fans
(1) Function: Installed at the kiln outlet to rapidly cool fired bricks. They may also assist in oxygen supply into the kiln, especially in long tunnel kilns, shortening airflow paths and improving efficiency.

5. Car-Bottom Balancing Fans / Kiln-Bottom Auxiliary Fans
(1) Function: Address poor ventilation at the car bottom by supplying cold air and coordinating with exhaust ducts to accelerate heat removal and prevent overheating of kiln cars.

6. Cooling-Zone Combustion Support / Rapid Cooling Fans
(1) Function: Combustion-supporting fans in the cooling zone provide oxygen supply, while rapid cooling fans quickly reduce temperature after the high-temperature zone to prevent over-firing of bricks. However, airflow must be precisely controlled during rapid cooling, otherwise it may cause cracks, dull sounds, and damage to product quality.

● Overall Roles of Fans in the Tunnel Kiln Firing Process
(1) Drying section: Dehumidification fans remove moisture and improve airflow, avoiding vapor accumulation.
(2) Preheating and firing section: Forced draft fans maintain oxygen supply; induced draft fans control airflow and pressure to ensure efficient combustion and uniform temperature.
(3) Soaking zone: Some systems place oxygen-supply fans at the top of the soaking zone to ensure complete combustion and waste heat recovery.
(4) Cooling section: Cooling fans or car-bottom fans rapidly reduce temperature and recover waste heat, contributing to energy saving and sustainable operation.

● Fan Selection and Configuration Recommendations
Fans should be selected according to different process stages: axial fans for drying, centrifugal forced draft/exhaust fans for firing, and axial fans at the outlet or kiln bottom for cooling.
(1) Temperature and medium characteristics: Select high-temperature and corrosion-resistant fan types to ensure long-term stable operation.
(2) Airflow and pressure matching: Airflow and pressure should be estimated based on fuel consumption and combustion air demand. A 50% capacity margin is recommended, with frequency control or belt adjustment for system optimization.
(3) Safety and quality assurance: Rapid cooling fans must maintain stable airflow to avoid structural damage to bricks; fan layout should also account for the kiln’s structural load-bearing capacity.

Compiled by: JF&Lou