News
Major research initiative completed
The lumber drying development projects carried out during the three-year Swedish IPOS research initiative crossed the finishing line in early 2020. In all, six sub-areas provided new knowledge that will help improve the drying process.
“It's not just about how quickly and energy efficiently we dry lumber, but also about intelligent automation with consistently high drying quality. When we take judicious steps along these lines, we create conditions for sawmills to increase their value yield,” says Thomas Wamming, Head of R&D at Valutec.
Thomas led the work, which included field studies at two Swedish sawmills, together with Margot Sehlstedt-Persson, Professor at Lulea University of Technology.
“We carried out full-scale industrial trials that would have been impossible without the contribution and commitment from the companies. It was truly impressive to see how smoothly everything went, and we would like to thank everyone involved,” says Thomas and Margot.
Shorter warm-up time
The studies also produced direct, concrete results. As a result of the sub-project linked to heating, tougher climates and shorter warm-up times have been introduced in Valmatics 4.0 for thin dimensions with a large sapwood content and a high initial moisture content.
“At the same time, it’s important to be aware of the raw material in the kiln. This is not a strategy for lumber that’s susceptible to checking such as coarse pine planks,” says Thomas.
Another project sub-area studied reversal intervals in batch kilns. In full-scale trials carried out during the project, data from trimmers provided feedback to the drying process. The issue evaluated concerned how an extended reversal interval during the drying phase would affect the moisture content accuracy and moisture content variation. To some extent, the study centered around reversal times that have always tended to be one hour in modern batch kilns. However, the effect of reversal time on lumber was not studied.
“Circulation fan rotation is easy to change in control systems. The outcomes can be implemented quickly where there are advantages to extending it,” explains Thomas.
Reversal
The study showed that extending reversal intervals to 6 hours both improved target moisture content accuracy and resulted in a smaller moisture content variation compared to normal reversal times of 2 hours. No increase in edge stack checking was noted in extended reversal intervals, which was a concern prior to the project.
"When it comes to wet dimensional lumber, we believe there to be advantages in prolonging reversal time up to six hours. The study also shows there to be no real disadvantages from prolonged reversal times in lumber of up to 50 millimeters, even if the effect is small when there is plenty of air across the full air-blow depth," says Thomas.
The sub-study was extensive. The drying tests were conducted in three modern batch kilns. Three different drying schedules were used with a total drying time of 60 hours and a target moisture content of 18 percent. The air-blow depth in the kilns was 10.5 meters, and each kiln had seven stacks.
The third sub-project also used measurement data from the trimmer as input to hone the drying process. It concerns time in the diffusion phase after an output drop while drying spruce board in a batch kiln. The goal here was to increase automation while retaining control over energy efficiency.
“The knowledge from this investigative study is a step on the way to our ultimate goal of developing Valmatics 4.0 as regards automating the process,” says Thomas.
Sub-studies included in IPOS
- Heating phase when drying spruce board. Initial studies in CT (scanner and tomography for material studies) with full scale industrial follow-up.
- Optimization of reversal intervals in batch kilns. Monitoring drying quality in trimmer data as feedback to the drying process. Full-scale industrial study.
- Time in the diffusion phase after an output drop while drying spruce board in a batch kiln. Monitoring drying quality in trimmer data as feedback to the drying process. Full-scale industrial study with a lab-scale follow-up in CT.
- CT‐studies into the conditioning stage following heat treatment according to the ThermoWood process.
- CT‐studies into moisture dynamics in an oscillating drying climate.
- Analysis of CT‐data during lumber conditioning. Calculating the moisture gradient from two previous projects.