This project evaluated a number of opportunities to coastal producers related to kiln drying issues such as drying practices related to high-value products, drying with superheated steam vacuum and internal core temperature monitoring for large timbers during the heat-up phase. In summary, this project included several laboratory studies to evaluate the using superheated steam/vacuum (SS/V) for drying 7/8”x 6, green western red cedar lumber, and 8x8 and 5x(5,6,7,8,9,10,12) Douglas-fir timbers. SS/V drying yielded faster drying schedules when compared to the results obtained in industrial conventional kilns. The results obtained from the SS/V drying of WRC indicated the potential benefits of technology for drying specialty products especially when compared to drying times obtained with conventional drying (longer than 7 days). However, the results obtained also emphasize the importance of green sorting that is, sorting prior to drying to optimize drying times and reduce the variation of final moisture content.
For large cross section Douglas-firs the drying times were between 3 and 14 days depending on the severity of the drying schedule and initial moisture content distribution. The influence of moisture content and cross section during the early and late stages of the heating process were evaluated on 5x5, 6x6 and 8x8 Douglas fir timbers. Thermodynamic equilibrium was reached after 20 hours regardless of moisture content or cross section size. The knowledge is intended to be used to design conventional drying schedules for large cross section timbers.
In British Columbia, due to the decline of lodgepole pine, mills should expect higher volumes of sub-alpine fir in their species mix. The impact on drying is significant. For example, drying times for green SPF (spruce, pine, sub-alpine fir) vary from 24 to 36 hours whereas drying times for sub-alpine fir can easily exceed 70 hours. In addition to longer drying times, the drying of species such as sub-alpine fir using current procedures often results in wet lumber and value loss can be higher than $100 per Mfbm. The potential annual impact for a typical BC mill is estimated to be in the range $1,000,000 to $1,500,000.
Along the years, sawmills have invested millions of dollars in drying technology (conventional drying and green sorting systems) which, for the most part are efficient and relatively low cost. Thus, under the circumstances outlined above, sawmills urgently need to find ways to minimize the problems associated with the drying of sub-alpine fir that is, new procedures or combination of methods, to ensure maximum grade recovery at the end of drying and reduce drying times (increase productivity and lower processing costs). In addition, the pressure exerted by typical longer drying times for sub-alpine fir will impact the drying of spruce and pine. Thus, strategies to speed the drying for those two species are needed to maintain annual production targets.
The main objective of this project is to evaluate several strategies using existing technology so that sawmills can readily implement them throughout their drying operations dealing with larger volumes of sub-alpine fir and for mills with kiln capacity constraints which could compromise their production targets.
According to the last forecasts released by BC Hydro, in 20 years the demand for electricity in B.C. will increase about 40%. A typical sawmill in Canada has between 4 and 8 kilns which operate on a constant basis throughout the year. Each kiln dries on average about 16 to 20 kiln charges per month and every kiln charge is on average 250 Mfbm of lumber (based on 2-inch thickness). A typical crossshaft kiln is equipped with fifteen 25 hp motors (approximately 18 kW) so the total installed power per
kiln is about 270 kW. Kilns operate an average of 660 hours per month. Thus, mills with drying operations such as in the example above will consume a significant amount of electricity to dry their
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