Photographer: Fredrik Persson

804 Recommendations for reducing the fan speed durin the wood drying Part 2

Published: 23 August 2012

The purpose of Part 2 of the project is to provide more detailed information on air speed adaptation to moisture departure will be implemented during the drying process. The goal is to create tools and recommendations on how to reduce the fan will be implemented with a reasonable margin of safety against production and quality problems.

Area: Measurement and Process
Budget: 775 000 SEK
Schedule: January - December 2011
Project Manager: Dennis Johansson, SP Wood / Thomas Wamming

Background

Energy and environmental issues are very important to the sawmills. The drying process is the most energy-intensive sawmill subprocess and requires both heat and electricity. Of the energy required to produce a finished wood product is drying to about 70%. When special study sawmills electricity consumption is the wiper circulation fans which is the largest consumer. In recent years the engine power of the circulation fans increased significantly and can be up to 90 kW in a large drying chamber.


The reason for sawmills install powerful fans that want a flexible chamber drier where it is possible to wipe both planks and boards with large variation in depth moisture. When drying wood with lower input moisture needed to the high air flow and thus can fans alternated down from the beginning of the drying process, with lower energy consumption as a result. The reason to want high air velocity is to ensure that the temperature drop is not too large. The risk is greatest during the part of the drying process when the free water is vaporized.


Consequently, an incorrect unwinding of the fans compromising the final quality of the dried product, with high quality costs as a result. There are other words, the risk of losing much more on defective products than you can save on energy consumption.


Important to remember is that we have a fleet of kilns on the Swedish sawmills that have wide range of ages. The older dryers from -80 and -90 century has no excess capacity of the fans, so there's no room to unwind except at nedtorkning below 18%.


An increased amount of air in the new wiper also depends on reducing drying times which has made the wipers must "go for the full" to handle the same amount of water in less time. Another reason for the higher air velocity is rapid moisture attrition that occurs in connection with drying at higher drying temperatures. Adjustment of air flow is drying and machine-specific and recommendations to operators must therefore be clear and clarify whether or how large reduction in air speed that is possible. We must not forget that an oversizing of air velocity provides a margin of safety that reduces the risk of problems such as the variation in depth moisture or amount of leakage air.


It is therefore important to develop knowledge and recommendations on how to save energy by reducing the fan speed without risking significant costs in terms of incorrectly dried or damaged timber.

Purpose, objectives

The purpose of Part 2 is to provide more detailed information on air speed adaptation to moisture departure will be implemented during the drying process. Greater emphasis on providing security operators in how to operate the wipers to save energy without causing problems in the drying process. The goal is to create tools and recommendations on how to reduce the fan will be implemented with a reasonable margin of safety against production and quality problems.

Reports

Previous projects in the field

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