Low-Temperature Drying of 4/4 Appalachian Red Oak

Low-temperature drying was evaluated as an alternative for conventional air-drying methods. Matched lots of green 4/4 red oak lumber were dried to 20 percent average moisture content in a low-temperature dryer and an adjacent air-drying yard. Low-temperature drying required 31 days for a 70?F. dry-bulb schedule, and 19 days for an 85?F. dry-bulb schedule. Air-drying required 61 days for lumber piled in June and July, and 138 days for lumber piled in November and December. Degrade losses were 0.9 percent of lumber value for the 70?F. dry-bulb schedule, and 0.5 percent of lumber value for the 85?F dry-bulb schedule. Air-drying degrade losses were 1.3 percent of lumber value for winter drying, and 1.6 percent of lumber value for summer drying. Drying costs per Mbf (excluding lumber handling and grading costs) were as follows: $17.87 for the 70?F. dry-bulb schedule; $12.19 for the 85?F. dry-bulb schedule; and $10.21 for air-drying. Even where exhaust or surplus steam would be, available for heat, the cost of low-temperature drying on the 70?F. dry-bulb schedule would exceed costs for the 85?F. dry-bulb schedule. Therefore, drying costs for the 85?F. dry-bulb schedule were used for further comparison with air-drying costs. Total drying costs (including degrade losses) were $13.04 per. Mbf for the 85?F. dry-bulb schedule and $12.67 per Mbf for air-drying, indicating a slight overall advantage for the air-drying method. However, the advantage was considered insignificant because degrade losses in commercial air-drying operations are generally higher than those experienced in the study. For commercial scale operations, the fixed capital required (initial investment plus average lumber inventory costs) for low-temperature drying would be 41.4 percent less than for air-drying.

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