PERFORMANCE OF INDUSTRIAL SOLAR KILN FOR DRYING TIMBER
M. N. Haque
Forest Research, NZ
&
T.A.G. Langrish
Department of Chemical Engineering,
University of Sydney
OutlineBackground to this researchDescription of this solar kilnMaterials and methodsActual measurements &
assessment of performanceComments on suitability in NZConclusions
Solar kilns for drying timber
Solar kilns for drying timber
Solar kiln at Boral Timber’s Herons Creek site, NSW, AUSTRALIA
Recent design of solar kiln by Solar Dryers Australia, Bellingen, NSW
Air-drying site
0
10
20
30
40
50
60
70
80
0 25 50 75 100 125 150 175 200
Time (days)
Moisture content (%)
Solar Air Kiln Kiln
Typical drying example
Materials & methods
Boral’s Solar Kiln
INPUTOUTPUTSOLAR KILN MODEL
Ambient T &
RH
Timber MC, air T & RH
0
20
40
60
80
100
0 20 40 60 80
Time (days)
T (oC) & RH (%)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
Moisture content (kg/kg)
Predicted RH
Predicted X
Actual X
Predicted TActual T
Actual RH
Timber properties
0
0.005
0.01
0.015
0.02
0.025
0 20 40 60 80
Time (days)
Instantaneous strain (m/m)
Quality prediction
Procedure for measuring MC
0
20
40
60
80
0 20 40 60 80
Time (days)
Moisture content (%)
Sample 1 Sample 2 Sample 3 Sample 4 Sample 5Sample 6 Sample 7 Sample 8 Average
Biscuit samples
Kiln sample boards
Biscuits30 cmKilnsample2 cm
• Biscuit samples: 2025043 mm, oven-dry test• Kiln sample boards: 30025043 mmestimated MC based on biscuit samples
Results- run 1 (May-June)
0
10
20
30
40
50
60
0 20 40 60
Time (days)
Temperature (
oC) & MC
(%)
Internal air Ambient MC
Results- run 2 (July-August)
0
10
20
30
40
50
60
70
0 20 40 60
Time (days)
Temperature (
oC)
& MC (%)
Internal air Ambient MC
Results- run 3 (Sep-Oct)
0
10
20
30
40
50
60
0 20 40 60
Time (days)
Temperature (
oC)
& MC (%)
Internal air Ambient MC
Results- run 4 (Nov-March)
0
10
20
30
40
50
60
0 20 40 60 80 100 120
Time (days)
Temperature (
oC)
& MC (%)
Internal air Ambient MC
Results- run 5 (March-May)
0
10
20
30
40
50
60
0 20 40 60 80
Time (days)
Temperature (
oC)
& MC (%)
Internal air Ambient MC
Results- summary
0
20
40
60
80
100
120
Run 1(May-June)
Run 2(July-Aug)
Run 3(Sep-Oct)
Run 4(Nov-
March)
Run 5(March-
May)
MC (%) &
Drying time (days)
Initial MC Final MC Drying Time
Measured solar radiation
0
200
400
600
800
1000
1200
1400
0 20 40 60
Days
Solar radiation (W/m
2)
Results- HEX status
0
1
0 10 20 30 40 50 60 70 80
Time (days)
Heat-ex status (1="On")
Image goes here
Some NZ facts About 2 million m3 timber dried each
year (mainly radiata pine) Average 3 GJ/m3 energy requirements Total 6 PJ energy consumption 95% thermal, 5% electrical 60% thermal from wood residue Processing of alternative species is
growing
Solar radiation at Rotorua, NZ (NIWA, 2002)
0.0
5.0
10.0
15.0
20.0
25.0
JanFebMarAprMayJun JulAugSepOctNovDecAnnual
Daily Radiation (MJ/m
2)
Image goes here
Initiatives in NZ
Greenhouse companiesRedpath: www.greenhouse.co.nzHarford: www.greenhouses.co.nz
Do not have drying tech experience but an engineering company can be brought together
Conclusions Solar energy, ambient T & RH, kiln T & RH and
wood MC were measured. Average increases in kiln air T (compared
with ambient) were: 17.3C (May-June) 13.8C (July-August) 10C (September-October) 8.2C (November-March) 7.5C (March-May)
Conclusions (continued) Drying times were 3 to 4 months from
initial (43 to 62%) to final MC (12 to 22%). Overall solar kiln is considered as an
acceptable alternative to air-drying method for pre-drying of hardwoods (e.g. blackbutt, Eucalyptus pilularis).
So Australasian timber industry is showing an increasing interest in use of solar kilns.
Acknowledgements
Boral Timber Division & Faculty of Engineering, The
University of Sydney for financial assistance