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Wood Sci Technol 37 (2003) 3–9 DOI 10.1007/s00226-002-0159-z Original Climate control in vacuum dryers for convective heat transfer Part 2: Actual climates in industrial kilns and suggestions to improve kiln design Bjo ̈rn A. Ka ̈llander 3 Abstract The first part of this contribution determined the demands on climate control in vacuum drying kilns that are necessary to achieve the final moisture content variation stipulated in the European Drying Group (EDG) proposal on wood drying quality standards. In this second part of the contribution, these demands are compared with measurements of actual climates and the resulting final moisture content in vacuum kilns during industrial production. The mea- surements show that none of the studied industrial vacuum kilns are capable of controlling climate with acceptable accuracy. The variations in drying climate lead to large variations in final moisture content and reduced production capacities. Drying quality and drying capacity would be greatly increased with improved kiln design and improved climate control systems. Critical factors in kiln design and climate control system design necessary to maintain a controlled drying climate are listed. Demands on temperature and pressure control In the previous part of this contribution (Ka ̈llander 2002) it was shown that the crucial factor in climate control is maintaining the set temperature. With a pressure control system capable of maintaining the pressure within ±0.1% of the set pressure, the temperature has to be maintained within ±0.8°C of the set temperature throughout the kiln to achieve the top drying class known as ‘‘Exclusive’’. The demands on temperature control to reach different drying classes are shown in Table 1. Received: 20 April 2000 Published online: 11 April 2003 Ó Springer-Verlag 2003 B.A. Ka ̈llander (&) Stora Corporate Research AB, 791 80 Falun, Sweden E-mail: bjorn.kallander@sp.se B.A. Ka ̈llander Building Material, Royal Institute of Technology, 100 44 Stockholm, Sweden Present Address: B.A. Ka ̈llander SP Swedish National Testing and Research Institute, Box 857, 501 15 Bora ̊s, SwedenPDF Image | Tech Table: Vacuum bagging supplies
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