Tunnel Drying Chamber Sectional Moisture Exhaust Fan

In China, some brick and tile plants use a counter-current tunnel dryer powered by waste heat from Hoffmann kilns to dry green bricks, enabling year-round production.

The tunnel drying chamber consists of 15 sections and uses one W9-57-101N16B centrifugal fan for centralized heat supply and another fan of the same model for centralized moisture exhaust. This air supply and exhaust arrangement has the following drawbacks:

1. Inconsistent moisture exhaust conditions, resulting in uneven drying of the green bricks. Drying proceeds faster near the exhaust fan and slower farther away.
2. Rapid corrosion of the exhaust fan impeller and casing; one impeller requires replacement in less than one year.
3. Replacement of a new impeller requires at least two days of intensive work, forcing shutdown of the brick machines and drying chambers, while the Hoffman kiln remains in a dormant, fire-stopped production state.

To address this issue, the factory drew on experience with axial-flow fans for sectional moisture exhaust. The motor was positioned outside the fan to prevent damage. Accordingly, a 45° cast-iron casing and cast-aluminum blades were designed, with the motor mounted externally on the moisture exhaust fan.

After adopting this fan, drying conditions in each tunnel section became uniform, significantly improving drying uniformity and efficiency, reducing power consumption and scrap losses, and eliminating production stoppages for fan maintenance. As shown in Table 6-2, sectional moisture exhaust using this fan offers clear advantages over centralized moisture exhaust.
Table 6-2

In summary, the results of sectional moisture exhaust are highly significant. However, the first-generation moisture exhaust fan still had the following shortcomings:

• The fan body was relatively bulky;
• Because the blades were located at the bottom, disassembly and replacement during maintenance were extremely inconvenient; operators had to squat inside the tunnel, where flue gas caused severe choking;
• Due to the motor being directly sleeved, after prolonged operation the lubricating oil in the bearings leaked out. When oil starvation occurred, the motor was prone to damage.

In response to the above issues, a horizontal 90° moisture exhaust fan was subsequently designed (Figure 6-10). After commissioning and trial operation, the results were excellent.

Figure 6-10 Schematic Diagram of Moisture Exhaust Fan

• 1—Electric Motor;
• 2—Belt Drive;
• 3—Impeller;
• 4—Air Outlet;
• 5—Flange;
• 6—Air Duct