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

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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

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Time (days)

T (oC) & RH (%)

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Moisture content (kg/kg)

Predicted RH

Predicted X

Actual X

Predicted TActual T

Actual RH

Timber properties

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0.025

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Time (days)

Instantaneous strain (m/m)

Quality prediction

Procedure for measuring MC

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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)

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Time (days)

Temperature (

oC) & MC

(%)

Internal air Ambient MC

Results- run 2 (July-August)

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Time (days)

Temperature (

oC)

& MC (%)

Internal air Ambient MC

Results- run 3 (Sep-Oct)

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Time (days)

Temperature (

oC)

& MC (%)

Internal air Ambient MC

Results- run 4 (Nov-March)

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0 20 40 60 80 100 120

Time (days)

Temperature (

oC)

& MC (%)

Internal air Ambient MC

Results- run 5 (March-May)

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Time (days)

Temperature (

oC)

& MC (%)

Internal air Ambient MC

Results- summary

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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

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Days

Solar radiation (W/m

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Results- HEX status

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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)

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JanFebMarAprMayJun JulAugSepOctNovDecAnnual

Daily Radiation (MJ/m

2)

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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