Forestry and Environment Sympoisum 1998, Sri Lanka

Fourth Annual Symposium organized by Department of Forestry and Environment Science, University of Sri Jayewardenapura, Sri Lanka.

Wednesday, October 04, 2006

DEVELOPMENT OF DRYING SCHEDULES FOR RUBBER AND PINE TIMBER FOR THE DEHUMIDIFICATION KILN DRYING

R S Sujith Rathnayake and H S Amarasekera
University of Sri Jayewardenepura,
Nugegoda.


Most of the timber in Sri Lanka is used in unseasoned state or seasoned using conventional kilns which use fuel wood boilers or open fires as a heating source. A study has been conducted to introduce dehumidification drying kiln, which is easy to fabricate and consumes less energy hence ideal for small scale timber industries.

Experiments were conducted to investigate drying behaviour, to develop kiln schedules and to evaluate the developed kiln schedules for Pine (Pinus caribaea) and Rubber (Hevea brasiliensis) timber. The dehumidification kiln used in the present study is locally fabricated and it has 25 cubic feet capacity. The temperature of the kiln can be increased to 50°C and relative humidity can be reduced to 16%.

Drying rate, percentage shrinkage and drying defects were observed for these two species by drying 21505000 mm stakes in temperature, humidity and air circulation controlled mini chamber. It was found that Pinus caribaea was relatively last drying timber compared with Hevea brasiliensis. However, H. brasiliensis showed higher percentage shrinkage and defects over P. caribaea during the early stages of drying. This indicates that H. brasiliensis should be dried slowly at the initial stages of drying.

Three kiln schedules with slow, medium and fast drying rates were developed for seasoning 25 mm planks based on the results of drying behaviour. Drying rate, drying efficiency, drying defects, drying cost and thermal efficiency of these kiln schedules were evaluated by drying 25xI50x1000 mm sample hoards in the dehumidification kiln. Compared with conventional kiln seasoning, dehumidification kiln seasoning gave higher duality dried timber with more than 90% drying efficiency and faster drying rate, while maintaining higher thermal and economical efficiency.

It is concluded that higher quality H. brasiliensis and P. caribaea dried timber can he obtained at a faster rate by drying them using these schedules in the dehumidification drying kiln compared with conventional drying.

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