Schedule Modification of drying rate to Decrease The drying time of juvenile Tectona grandis L. wood
Keywords:
kiln drying, energy consumption, Dry-bulb temperature, wet-bulb temperature, wood dryingAbstract
The authors investigated modifying schedules to increase the drying rate (DR) and reduce the total drying time for Tectona grandis L. wood from juvenile plantations. The initial MC ranged from 92 to 115%. A conventional teak schedule was used as the basis for developing two faster drying schedules and for comparison. The modifications resulted in a reduction in drying time from 125 to 105 hours, a 16% energy savings and less than 1% MC variation in dried lumber; however, this change caused a slight decrease in wood quality. The relationship between the DR, the lumber's MC, and drying time was modeled. As expected, the dry-bulb temperature and wet-bulb depression had the greatest influence on DR; however, an inflexion point was found in the relationship between DR and MC at a 40% MC for all three drying schedules. The inflection point indicates when diffusion becomes the primary driving force of moisture movement, therby llimiting the DR, and indicating when the kiln conditions should be accelerated to minimize the total drying time. DRhour should remain over 0.5%/hour (high value for tropical species) for the first 72 hours (3 days), until the lumber reaches 40% MC and then be lowered to 0.5%/hour until drying is completed.
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