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For. 486, Lecture 3-7

For. 486, Lecture 3-7. Fiber, particle, and flake drying. DRYING EQUIPMENT FOR PARTICLES AND FIBERS. All of these systems generally use high temperatures and short drying times (~10 sec to 10 min). ROTARY DRYERS. Rotating drum Particle, flake, and strand drying Single- and triple-pass.

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For. 486, Lecture 3-7

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  1. For. 486, Lecture 3-7 Fiber, particle, and flake drying

  2. DRYING EQUIPMENT FOR PARTICLES AND FIBERS All of these systems generally use high temperatures and short drying times (~10 sec to 10 min) ROTARY DRYERS Rotating drum Particle, flake, and strand drying Single- and triple-pass JET DRYER Fixed drum with high air velocity Particle drying BUNDLE-TUBE DRYER Fixed drum with interior rotating bundle of heated tubes No direct contact with heating medium Particle drying FLASH-TUBE DRYER Long fixed tube (100 to 200 ft.) High velocity air for heating and pneumatic conveyance Fiber drying TRAY DRYER Trays comprised of porous screens move inside a heated tunnel Flake and strand drying Lower temperature than rotary dryers Slide courtesy Dr. Fred Kamke, Virginia Tech

  3. Single-Pass Tube Dryer (fiberboard) Initial MC, approx 50%, final, 8-12% Air/fiber ratio, 50 ft3/lb; 3,000 fpm air velocity Wet end temp, 500-650 oF Exit temp, 150-190 oF; drying time 5 sec.

  4. Multiple-pass Tube Dryer (fiberboard) Useful for furnish with large variation in MC

  5. High Temperature Fiber Dying: Considerations • Fire and explosion hazard – adequacy and maintenance of fire detection and suppression systems cannot be overemphasized!! • Particulate and VOC/HAP emissions • Danger of resin pre-cure in tube dryer (blowline application of resin) • Rotary fiber dryers have been used, but drying tubes/blowlines are most prevalent

  6. Flake/Particle Rotary Drum Dryer Inlet temperature may vary with furnish MC: 175%MC, 1800 oF inlet; 67-100% MC, 700-1200 oF Furnish residence time, 5-6 minutes; 30,000 lb H2O removal /hr.

  7. Cut-Away Diagram of Drum Dryer

  8. Three-Pass Drum Dryer • Furnish starts in center, then intermediate, then outer drum cavity as it dries to 3-4% MC

  9. ROTARY DRYER (Bison) ROTARY DRYER (MEC) Rotary dryers are used for particles, strands, and hog fuel. Slide courtesy Dr. Fred Kamke, Virginia Tech

  10. Rotary Dryer with Particle Collectors Slide courtesy Dr. Fred Kamke, Virginia Tech

  11. Rotary Dryer with Particle Collectors Slide courtesy of Metso Panelboard

  12. VOC Reduction Technology • Recent research has shown that multi-stage drying, starting with low temperature (70-150 C), may be used to first generate, concentrate, and collect for combustion a high proportion of VOCs. This could obviate (eliminate) the need for expensive emission control devices such as RTOs. • Banerjee et al., 2000. Method of lowering the VOCs emitted during drying of wood products. U.S. Patent No. 6,029,368.

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