Wood Research Centre2

Department of Wood and Forest Sciences, Laval University, Quebec (Qc), Canada G1K 7P4

Potential of High-Temperature Drying for the Production of Value-Added Products

Yves FORTIN* and Aziz LAGHDIR

Slovakia

European Union

Quebec

Wood Research Centre

Aim of work and methods

3

To study the potential of high temperature drying for the manufacturing of value-added products from wood species traditionally used for construction lumber:

Development of drying programs and strategies Evaluation of drying time, quality of the dried products and energy

consumption

Wood Research Centre

Aim of work and methods

3

Wood species and experimental procedure

Species Dimensions Top loading Drying process (kN/m2) Black spruce (Picea mariana) 50 x 75 x 2400 mm 1.2 & 9.8 HTD White spruce (Picea glauca) 50 x 100 x 2400 mm 7.2 HTD Balsam fir (Abies balsamea) 50 x 100 x 2400 mm 7.2 CTD/HTD ;

HTD Tamarack (Larix laricina) 32 x 100 x 2400 mm 7.5 CTD ; ETD ;

HTD Trembling aspen (Populus tremuloides) 50 x 100 x 2400 mm 7.2 CTD/HTD ;

HTD

Wood Research Centre

Aim of work and methods

3

Experimental 2.5 m3 capacity kiln

Wood Research Centre

Aim of work and methods

3

Typical HT drying schedule

StepTime (h)

MC range (%)

Dry bulb temperature

(oC)

EMC (%)

Preheating 4 97 18

Presteaming 10 95 --

HT drying step 1 >35 105 7

HT drying step 2 35-8 115 3

Cooling 2 115-90

Equalizing 15 90 7

Conditioning 4 90 11

Cooling 3 40

Wood Research Centre

Results

4

Comparison of drying time

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140

Time (h)

Mo

istu

re c

on

ten

t (%

)

White spruce

Balsam fir (normal heartwood)

Trembling aspen (normal heartwood)

Black spruce

Wood Research Centre

Results

4

Comparison of drying time

0

20

40

60

80

100

120

0 25 50 75 100 125 150 175 200 225 250

Time (h)

Mo

istu

re c

on

ten

t (%

)

Balsam fir (normal heartwood)

Trembling aspen (normal heartwood)

Trembling aspen (sinker heartwood)

Balsam fir (sinker heartwood)

Wood Research Centre

Results

4

Comparison of drying time

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120 140 160

Time (h)

Mo

istu

re c

on

ten

t (%

)

CTD (Tamarack)

ETD (Tamarack)

HTD (Tamarack)

Wood Research Centre

Results

0

1

2

3

4

5

6

7

8

Bow (mm) Crook (mm) Twist (mm)

HTD – 1,2 kN/m2 (Black spruce)

HTD – 9,8 kN/m2 (Black spruce)

4

Warp and grade fall-down

0

5

10

15

20

25

30

35

Grade fall-down(%)

Wood Research Centre

Results

4

Warp and grade fall-down

0

1

2

3

4

5

6

Bow (mm) Crook (mm) Twist (mm)

HTD (Tamarack)

ETD (Tamarack)

CTD (Tamarack)

0

5

10

15

20

25

30

Grade fall-down (%)

Wood Research Centre

Results

4

Effect of sinker heartwood on the final moisture content (FMC) distribution

0

2

4

6

8

10

12

14

FMC-mean FMC-variation

Balsam fir mixed heartwood (HTD)

Balsam fir sinker heartwood (CTD/HTD)

Balsam fir normal heartwood (HTD)

Wood Research Centre

Results

4

Total shrinkage following kiln drying

1 50 x 75 x 2400 mm black spruce kiln dried to 10% MC 2 50 x 100 x 2400 mm plantation white spruce kiln dried to 10%

Tang. (%)

Radial (%)

Width (%)

Thickness (%)

Width (%)

Thickness (%)

4.72 2.39 3.661 4.041 3.561 4.431

4.34 2.01 3.112 3.072 2.602 3.972

Free shrinkage

CTD

(Tmax = 82oC)

HTD

(Tmax = 115oC)

Wood Research Centre

Results

4

Energy consumption at the kiln

0

100

200

300

400

500

600

700

800

900

Preheating ofwood

Preheating ofthe kiln

Preheating ofwater and

evaporation

Preheating ofair and

humidification

Heat losses bythe kiln

Electricalenergy for air

movement

Corrected totalheat

consumption

Energy consumption at the kiln (MJ/m3) - CTD (Balsam fir)

Energy consumption at the kiln (MJ/m3) - HTD (Balsam fir)

Wood Research Centre

HTD has a great potential for the drying of value-added products;

HTD saves time, electrical energy and can help to control drying defects for warp prone species;

Conclusions

Wood Research Centre

HTD must be combined with CTD for species containing impermeable sinker heartwood;

A proper strategy of HTD must provide for the use of top-load restraint, presteaming treatment, long equalizing period, conditioning, and a slightly increased green dimension in thickness.

Conclusions

The authors thank Mrs. Gordon Duplain, Bruno Girard, Abdelkarim Ben Mhenni, and Javier Chung, former graduate students, for their contribution to this paper.