BC Coastal mills will need to diversify the drying technologies currently used and consider new approaches in order to improve productivity, reduce drying costs, regain competiveness and continue to play a significant role in the increasingly stringent quality market for forest products. New demands for drying are related to energy efficiency, low environmental impact and of course, quality of the final product.
The specific objectives of the project were: (1) to improve the conventional drying of 4.5” x 4.5” Douglas-fir lumber, (2) to evaluate the superheated steam/vacuum (SS/V) drying of 4.5” x 4.5” Douglas-fir lumber, (3) to develop a green sorting strategy for hem-fir lumber and (4) to determine the time required to reach 56°C in the core of 5¼ x 5¼ lumber using the requirements of CFIA PI-07 Heat Treatment schedule Option D - Generic Phytosanitary Heat Treatment Schedule, Heat Treatment with Moisture Reduction.
The results showed that the drying time in conventional drying of 4.5” x 4.5” Douglas-fir lumber can be reduced by up to 25% without compromising the quality of the lumber. This can be achieved by increasing the temperature in the final drying stages and using lower relative humidity at the beginning of the drying process. In addition, final moisture content (MC) variation was reduced from 6.2% to 3.9%.
Reductions of drying times from 26% to 41% were observed when drying 4.5” x 4.5” Douglas-fir under SS/V drying. Quality of the lumber at the end of drying was better when compared to the quality of the lumber at the end of conventional drying. In addition, specimens exhibited less final MC variation.
Based on drying rate measurements of green hem-fir lumber dried to 9.0% MC, a new database was developed which in turn was incorporated into OASiS 2.0 software to evaluate different pre-sorting scenarios. Pre-sorting simulations allow end users to estimate the impact of kiln productivity, final MC distribution and drying degrade. The results showed that different correlations between the time to reach 19.0% MC and initial weight or initial MC could be established. The best correlation with an R square of 0.77 was made between initial weight and MC. After performing several simulations with the new database an optimum cut-off point of 65% yielded the best results in terms of potential increase of productivity and quality of the final product.
Wood heating rate test results showed that CFIA Option D may be extended for 5¼ x 5¼ lumber as long as the dry-bulb = 71°C (= 160°F) for 36 hours at the end of the heat treatment. Total heat treatment time required, including the time required to reach 71°C (160°F), is 72 hours.