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- Hägg, Linus, et al.
(författare)
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Influence of Fan Speed on Airflow distribution in a Scandinavian Drying Kiln
- 2012
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Konferensbidrag (refereegranskat)abstract
- From the beginning of the 90’s the development of drying kilns in Scandinavia has been focusing on increased drying capacity and also making the kilns more flexible in terms of handling differences in dimensions and initial moisture content. In order to facilitate the demand of higher airflows there has been an increase in circulation fan capacity. In a sawmill with modern kilns the fan capacity in a single batch kiln can be over 90 kW, making the drying kiln fans the single biggest consumer of electric power.Today, more and more sawmills are reviewing their consumption of electric power due to increasing prices. One way of reducing the consumption is to reduce the fan speed when the moisture content is so low that the drying rate is mainly limited by the diffusion properties of the wood and not the airflow. Since modern kilns are designed for high capacity fans there is a lack of knowledge of how a reduced fan speed affects the airflow distribution. This poses a risk of getting reduced quality of the final product due to increased moisture content variation in a batch.In this study the airflow has been measured inside an industrial drying kiln. For this study two experiments were done with 20 airflow gauges placed inside a kiln. During both experiments the kiln was fully loaded with pre dried Scotts pine (Pinus sylvestris) boards with a thickness of 50 mm. The reason for using pre-dried boards was simply that the gauge was not able to withstand the climate produced during a real process. In order to cover as much of the kiln as possible the gauges were distributed differently for the two experiments.The results show that about 30 % of the total airflow passes through the bolster spaces which are only about 20 % of the total flow area. This means that a notable volume of air might not be participating in drying of the boards.The results show also that the relative airflow distribution between the middle and the side of board stacks becomes more heterogeneous at a low fan speed. This trend is also seen for the relative distribution of airflow between bolster and sticker spaces.
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