Continuous tunnel kiln direct-fired with bark to dry 1.75-inch southern pine in 12 hours

Abstract

Length-sorted lumber is surfaced on one side to 1.75-inch thickness, mechanically stacked 5 feet wide and 10 feet high on 1-1/4-inch-thick sticks, and continuously transported through a zone-controlled tunnel kiln at 8 ft./hr. to yield 500,000 fbm of lumber dried to 9 percent average MC per 168-hour week. In the tunnel, the lumber is dried for 8 (possibly 10) hours of 270°F, conditioned for 3 hours at 195°F, and cooled for 1 hour before discharge to cooling sheds and subsequent unstacking. During drying and conditioning, wet-bulb temperature is held constant at 185°F. air velocities vary by zone; i.e., 1,600 fpm at inlet, 300 fpm while conditioning, and 1,000 fpm while cooling. To control warp, a top load (12 in. of concrete) is automatically placed on the moving lumber stacks as they enter the tunnel kiln and removed as they exit.

Citation

Koch, Peter; Wellford, Walker L., Jr. 1976. Continuous tunnel kiln direct-fired with bark to dry 1.75-inch southern pine in 12 hours. Forest Products Journal, Vol. 27(5): 39-47