Papers Proceedings »
SOLAR DRYER FOR SAWN LUMBER: TECHNOLOGY FOR THE SMALL AND MEDIUM FOREST INDUSTRY
The small and medium sized forestry enterprises lack of infrastructure to dry their sawn lumber, they have as a limiting the low financial capacity to purchase expensive drying equipment, as a result they offer wet lumber or air-dried-lumber. They have as a viable option the use of solar dryer, for its low investment cost, ease of operation, use of renewable energies as a source of heat, with temperatures up to 60 ºC. Prototype of 7m wide × 12m length, (60m2 solar collector) with a rectangular tubular profile structure, covered with polycarbonate sheets and fans to move a volume of air of 80 m3 was designed and built in Zacatecas, Mexico, also its efficiency was assessed. A 4.5 thousands of board foot(fb) of 1 inch thick of pine lumber were dried, with commercial widths of 6, 8, 10, 12 in and 16 ft length, at 78% of initial moisture content(CH). The temperature, relative humidity(RH) and CH of lumber were monitored to evaluate quality, costs, time and speed drying. The internal chamber conditions during the day were temperatures between 19 to 59ºC versus 14 to 42 ºC ambient-temperature; RH between 10 to 70% versus 22 to 90% ambient-humidity. The drying times at 12% of CH in winter, spring and summer were 24, 20 and 18 days, respectively. 95% of the boards maintained a prime and better quality; while 5% presented bowing. The drying speed was determined at 0.160 Kg of water/h m2 of green wood at 30% CH and 0.055 Kg of water/h m2 at 12% CH. The dried costs were $1.55 mexican pesos/fb, the economic recovery of the investment was at the 9th of the 18 drying processes feasible to perform annually. The solar dryer assessment achieves a good technical-economic efficiency and the feasibility of being used in these forestry enterprises.