Functions and Working Principles of Core Ventilation Equipment in Tunnel Kiln Automatic Control Systems
The stable and high-efficiency operation of a tunnel brick firing kiln depends entirely on a precise tunnel kiln automatic ventilation control system. Two core ventilation devices, the tunnel kiln exhaust fan and heat extraction fan, undertake critical production tasks including kiln oxygen supply, combustion supporting, heat transmission and drying air supply. These two fans are core components of brick and tile production lines, which directly affect tunnel kiln firing stability, green brick drying effect and finished brick quality. Understanding their professional working principles is essential for standardized and intelligent tunnel kiln production for global brick manufacturers.
The exhaust fan serves as the core power source for tunnel kiln combustion and internal heat circulation in the automatic control system, with two indispensable core functions.
Firstly, it provides stable oxygen supply for high-temperature firing inside the tunnel kiln and continuously delivers hot air to the drying chamber for green brick drying. The exhaust fan extracts internal flue gas and circulating air through wind brakes installed in the tunnel kiln’s cooling zone, heat preservation zone, combustion zone and low-temperature preheating zone. The internal airflow moves opposite to the traveling direction of green bricks, forming a scientific countercurrent heat exchange structure that improves overall heat utilization efficiency.
Secondly, the exhaust fan transports high-temperature waste flue gas from the tunnel kiln to the drying room, realizing waste heat recycling and providing a stable and continuous heat source for green brick drying.
In the low-temperature preheating zone of the tunnel kiln, hot airflow extracted by the exhaust fan continuously transfers heat to newly entered green bricks, raising the brick temperature to the ignition point of internal mixed coal. Once the internal coal ignites, sustained combustion rapidly raises the tunnel kiln temperature to the maximum firing temperature of approximately 1000℃. Professional tunnel kiln operation requires precise matching between exhaust fan air volume and internal coal feeding quantity, which maintains optimal oxygen content in the combustion zone. This ensures 70% to 80% of the mixed coal is fully burned in the combustion zone, allowing bricks to enter the subsequent heat preservation and cooling zones for stable temperature shaping. In the heat preservation and cooling zone, high-temperature sintered bricks transfer residual heat to circulating air, further increasing airflow temperature to support secondary combustion in the tunnel kiln combustion zone.
Unmatched exhaust fan air volume is a major cause of various tunnel kiln firing defects and unstable product quality. Insufficient exhaust air volume leads to incomplete coal combustion and insufficient heat output, causing typical firing problems such as slow front fire advancement, unretracted rear fire, and surface fire accumulation without bottom fire penetration. On the contrary, excessive exhaust air volume results in massive heat loss carried by flue gas. Although the front fire moves fast and the rear fire retracts timely, the overall tunnel kiln temperature drops sharply, forming bottom fire without surface fire and seriously reducing finished brick qualification rate.
Different from the exhaust fan, the tunnel kiln heat extraction fan only focuses on heat extraction and hot air delivery for drying purposes, without participating in kiln combustion oxygen supply. It extracts residual hot air from the tunnel kiln cooling zone and delivers it to the drying room to finish green brick drying. The airflow direction of the heat extraction fan is opposite to that of the exhaust fan, creating a mutually restrictive airflow balance relationship in the tunnel kiln automatic control system. Increasing heat extraction air volume reduces the temperature of the cooling zone, heat preservation zone, combustion zone and preheating zone; reducing heat extraction volume raises the temperature of all tunnel kiln zones. Excessive heat extraction will occupy the exhaust fan air volume, cause overall kiln temperature drop, and easily trigger production anomalies such as stagnant firing fire and overfired bricks in the middle of the kiln car, bringing quality risks to large-scale brick production.
